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LIPPriVCOTT'S   PHrSIOLOGTES 


THE  THIRD  BOOK 


OF 


ANATOMY,   PHYSIOLOGY 

AND 

HYGIENE 

OF    THE    HUMAN     BODY 

BY 
J.  A.  CULLER,  Ph.D. 

PROFESSOR     OK     PHYSICS     IN     MIAMI     UNIVERSITY,     OXFORD,     OHIO 


PHILADELPHIA  AND  LONDON 
J.   B.  LIPPINCOTT    COMPANY 


Copyright,  1904,  by  J.  B.  Lippincott  Company 


Copyright,  1905,  by  J.  B.  Lippincott  Company 


We,  the  undersigned,  have  carefully  read  Book  III.  of  the  Lippin- 
cott Physiologies,  and  are  happy  to  note  the  full  and  adequate  teaching 
of  the  physiological  reasons  for  obeying  the  laws  of  health,  including 
those  that  relate  to  the  nature  and  effect  of  alcoholic  drinks  and  other 
narcotics  upon  the  human  system  which  this  book  contains. 

The  truths  taught  are  well  told  in  language  adapted  to  pupils  in 
elementary  and  secondary  schools,  for  which  we  heartily  recommend 
the  book. 


Mary  H.  Hunt, 

Life  Director  of  National  Educational 
Association ;  National  Director  of  Bu- 
reau of  Scientific  Temperance  Investi- 
gation, and  World  and  National  Super- 
intendent of  Department  of  Scientific 
Temperance  Instruction  of  the  Wom- 
an's Christian  Temperance  Union. 


Members  of  the  Text-Book  Covunittce 
of  the  Advisory  Board 

George  W.  Webster,  M.D., 

President  of  Illinois  State  Board  of 
Health. 

Lewis  D.  Mason,  INLD., 
T.  D.  Crothers,  M.D., 

Professor  of  Diseases  of  the  Brain 
and  Nervous  Sj'stem,  the  New  York 
School  of  Clinical  Medicine. 

Rev.  Albert  H.  Plumb,  D.D. 
William  A.  Mowry,  Ph.D. 


Electrotyped  and  Printed  by 
J.  B.  Lippincott  Company,  Philadelphia,  U.  S.  A, 


PREFACE 


This  is  the  last  book  of  a  series  of  three.  It  is  the 
most  advanced  of  the  tliree,  and  is  complete  within 
itself.  It  is  intended  to  embrace  the  facts  in  anatomy, 
physiology,  and  hygien*e  which  every  man  and  woman 
shonld  know. 

Every  effort  has  been  put  forth  to  make  the  subject 
plain  to  the  reader.  This  is  important  in  a  subject  of  this 
kind.  A  lack  of  interest  very  frequently  arises  from  the 
inability  to  grasp  an  idea  as  it  is  presented,  though  it 
may  be  simple  enough  when  presented  in  a  different  way. 

The  body  is  treated  as  an  organized  unit,  each  part 
having  a  function,  and  all  parts  being  related  to  the 
others  and  dependent  upon  the  harmonious  operation  of 
all.  The  division  of  labor  among  the  organs  of  the  body 
is  often  so  sharp  that  a  derangement  of  one  tends  to  a 
disorganization  of  the  whole  body.  This  furnishes  a 
strong  basis  for  rules  of  hygiene  and  the  consideration 
of  the  alcohol  problem. 

This  book  contains  not  only  general  statements,  but 
exact  information  as  far  as  possible.  Technicalities  may 
seem  to  be  avoided  by  general  statements,  but  the  subject 
is  thus  often  robbed  of  its  interest  and  value.  The  red 
corpuscles  are  the  carriers  of  oxygen,  but  in  a  book  of 
this  kind  the  function  of  the  hemoglobin  and  its  affinity 

iii 


iv  PREFACE 

for  oxygen  should  be  explained.  Otherwise  the  pupil 
may  get  the  idea,  as  in  cases  known,  that  the  gas  is 
carried  in  the  concave  depression  of  the  corpuscle.  This 
is  an  illustration  of  the  many  peculiar  ideas  which  pupils 
form  fi'om  only  general  statements. 

Questions  are  appended  at  the  end  of  each  chapter. 
These  are  mainly  topical.  It  is  i^resumed  that  the 
teacher  will  add  numerous  questions  in  the  nature  of 
quizzes,  as  conditions  may  demand,  but  the  best  recita- 
tion is  one  in  which  a  pupil  discusses  a  topic  in  a  con- 
nected discourse. 

A  list  of  experiments,  such  as  may  be  performed  in 
any  school  where  this  book  is  used,  is  found  at  the  end 
of  each  chapter.  The  experiments  are  i^urposely  few  in 
number,  being  selected  with  the  intention  that  not  one 
of  them  need  be  omitted.  It  is  better  to  give  them  from 
time  to  time  during  the  study  of  the  text,  rather  than  all 
at  once.  The  teacher  will  find  it  profitable  to  supple- 
ment the  list  with  others  when  time  and  conditions  per- 
mit. Nothing  is  so  great  an  aid  in  making  this  subject 
interesting  as  ex|3eriments  which  are  performed  by 
teacher  and  pupils.  Many  experiments  may  be  per- 
formed at  home,  and  will  be  performed  with  zest  by 
most  of  the  class  after  they  have  had  proper  direction. 

The  subject  of  alcohol  and  its  effect  on  the  body  has 
been  treated  in  the  light  of  modern  investigation.  The 
statements  in  regard  to  its  effect  are  based  upon  a  knowl- 
edge of  the  nature  of  the  human  organism,  reliable 
experiments  which  have  been  made,  and  the  experiences 
of  the  past. 


PREPArn^:  V 

The  writer  acknowledjj^es  his  iiulel)tedness  to  tlie  J.  B. 
Lippincott  Company  for  many  courtesies,  and  permission 
to  use  a  number  of  cuts  belonging  to  tliem.  Also  te 
S.  II.  Williams,  professor  of  biology  in  Miami  Univer- 
sity, for  many  valuable  suggestions  and  reading  of  man- 
uscript, and  to  G.  W.  Hoke,  professor  of  natural  history 
in  Miami  University,  for  many  helps  and  suggestions. 

By  permission  of  Ginn  &  Co.  two  cuts  from  BlaisdelPs 
physiology  are  used  in  this  text. 


TABLE  OF  CONTENTS 

Cn.vrTER  PAGE 

I.  (Jeneraf,    \'iew  of  the  Subject 5 

II.  The  Cells  of  the'  Body l-*^ 

III.  The  Skeletox      3^ 

IV.  Structure  and  Nourish :sient  of  Bones 45 

V.  Joints -^'^ 

VI.  -Motion     ''^^' 

VII.  Foods '^ 

VIII.  Digestion ^'^ 

IX.  Wholesome  and  Unwholesome  Drinks 118 

X.  Circulation       1-^ 

XI.  Respiration ^^'"-^ 

XII.  Bacteria      ^^-^ 

XIII.  The  Skin 207 

XTV.  Excretion       --^ 

XV.  The  Xervous  System 231 

XVI.  Physiology  of  the  Xervous  System 258 

XVII.  Hygiene  of  the  Xervous  System 271 

XVIII.  The  Special  Senses 293 


Vll 


LIST  OF   ILLUSTRATIONS 

¥ 

FIG.  PAGE 

1.  Typical  coll \:i 

2.  Collection  of  plant-cells 14 

3.  kSection  of  twig  of  basswood 14 

4.  Section  of  pinewood !."> 

5.  Stomata  of  leaf 13 

6.  Bone-cells       10 

7.  Multiplication  of  cells  from  a  single  cell 17 

8.  Cell  under  a  strong  microscope 17 

9.  Protozoa     . 19 

10-15.  Stages  of  cell  division 20 

16.  The  amoeba  radiosa 22 

17.  Pavement   epithelium 24 

18.  Columnar  epithelium 24 

19.  Ciliated  epithelium 2.5 

20.  Tvpe  of  gland 29 

21.  Human  skeleton       34 

22.  Longitudinal  section  of  bone 37 

23.  The  cranium 38 

24.  A  vertebra 39 

2.5.  The  atlas 39 

26.  The  axis 40 

27.  The  sacrum  and  coccyx 40 

28.  The   spinal   column 41 

29.  Tlie   ribs 42 

30.  The  forearm  and  lower  leg 43 

31.  Section  of  flat  bone 45 

32.  ^klagnified  .section  of  bone 46 

33.  Bone  tied  in  knot 48 

ix 


X  LIST   OF   ILLUSTRATIONS 

FIU.  PAGE 

34.  The  hip-joint oo 

35.  Pivot-joint 5G 

3G.  Muscular    movement 60 

37.  Bones  of  arm  and  biceps  muscle 61 

38.  Levers  of  first  class 62 

39.  Levers  of  second  class 64 

40.  Lever  of  third  class 64 

41.  Shape  of  muscle 66 

42.  Fascia  of  muscle 67 

43.  Muscles  of  forearm 68 

44.  Striated  muscle  fibres 69 

45.  Involuntary  muscle  fibres 69 

46.  Exercisers      72 

47.  Trichinae  in  pork 90 

48.  Osmosis    of   liquids 95 

49.  Permanent  teeth 98 

50.  Section  of  tooth      99 

51.  Magnified  section   of  tooth 99 

52.  Racemose    gland 100 

53.  Stomach  and  intestines 103 

54.  ^lucous  coat  of  stomach 104 

55.  Section  small  intestine  of  cat 107 

56.  Microphotograph  of  villi       107 

57.  Diagram  of  villus 108 

58.  External  view  of  liver 109 

59.  Lobule  of  liver 109 

60.  Shallow    wells 125 

61.  External  view  of  heart 131 

62.  Cavities  of  heart 132 

63.  Auriculo-ventricular  valves      133 

64.  Section  of  heart       133 

65.  Semilunar  valves 134 

66.  Showing  course  of  blood  through  heart 135 

67.  Section  of  artery  and  vein 136 


LIST    or    IFJJ'S'njATIoNS  xi 

fl»'-  PACK 

(is.   (  iipilliirics \im 

(59.  C'apillaiit's   in    miisclc i;jS 

70.  IJrd    l»l(i<t(lc((||)uscl('s        I  j;; 

71.  Microphotoj^rapli  of  red  coi  pii^clcs 1  i;; 

72.  Scctidi)   llirouiili  vent ri('lf'.>  of  licail 140 

7.*{.  Selii'iiu'  showiii^^  circulation  of  blood 14S 

74.  The  fluco  envelopes  of  the  eartli liiJ 

1'}.  Tlie  laiyiix 100 

70.  The  vocal  cords 100 

77.  The  trachea  and  bronchi. 107 

78.  Infundibiila  and  air-sacs       108 

79.  The  lungs       109 

80.  The  pleura 170 

81.  Illustration  of  action  of  ribs 172 

82.  Illustration  of  action  of  diaphragm 17.3 

8.3.   Illustration  of  the  combustion  of  iron 17.3 

84.  Illustration  of  changes  in  a  leaf 177 

8,1.   Ivxchanges  in  the  lungs 178 

SO.   Dillusion    of  gases 178 

87.   Window  arranged  for  ventilation       182 

SS.    Particles  of  dust 184 

89.  Action  of  intercostal  muscles      190 

90.  Bacteria      192 

91.  Multiplication  of  bacteria 193 

92.  Yeast-plants       193 

93.  Bacteria  of  diphtheria 198 

94.  Bacteria  of  lock-jaw 199 

9.5.  Bacteria  of  tuberculosis 200 

9G.  Bacteria  of  typhoid  fever 201 

97.  Cross-section  of  skin  of  monkey's  linger 207 

98.  Magnified  cross-section  of  skin 209 

99.  Surface  of  palm  of  hand 210 

100.  Sweat-glands -H 

101.  Hair-follicle       213 


xii  LIST   OF   ILLUSTKATIONS 

^I<5.  PAGE 

102.  Cross-section  of  kidney 224 

103.  Section  of  cortex  of  kidney 22.j 

104.  Malpighian  body 220 

105.  Malpighian    bodies 227 

lOG.  Neurons      234 

107.  A  neuron 230 

108.  Medullated  nerve-fibre 230 

109.  Neuralgia  cells 237 

110.  Brain  on  right  side 239 

111.  Top  of  cerebrum 240 

112.  Section  of  brain,  left  half 241 

113.  Convolutions 242 

114.  Section  of  nerve 244 

115.  Section  of  spinal  cord 248 

IIG.  A  piece  of  spinal  cord 249 

117.  Cervical  nerves 250 

118.  Relation  of  nerves  from  spinal  cord 251 

119.  Communication  of  neurons 252 

120.  End  plate       252 

121.  Connection  of  nerve  and  muscle 253 

122.  Branching  of  nerves 254 

123.  Motor  and  sensory  areas  of  brain 2G0 

124.  The  supply  of  blood  to  the  brain 274 

125.  Fatigued   cells 275 

126.  Section  of  the  eye 297 

127.  Illustrations  of  refraction 299 

128.  Influence  of  cornea 300 

129.  Function  of  iris 301 

130.  Attachment  of  lens 303 

131.  Focal  distance       304 

132.  Convexity  of  lens 304 

133.  Emmetropic    eye 305 

134.  Myopic  eye 306 

135.  Hypermetropic  eye 307 


LIST    or    ILf.rSTIJATIoXS  xiii 

rir..  PACK 

l:{t>.   .Musflfs  t)l  ryt'       :iOS 

1.57.  Nerve  elements  of  retina ;ilO 

13S.   Rod  and  cone 311 

130.  Retina 312 

140.  Optic  nerves      :;14 

141.  Tear   f,'lan(Is 317 

142.  Sound-waves      320 

143.  Pinna  of  ear     . 322 

144.  Drum-head  and  ossicles  of  ear 323 

145.  Mechanical  action  of  tympanum 32.j 

14G.  Section  of  ear 32S 

147.  Labyrinth  of  ear      329 

148.  The  cochlea 331 

140.  The  membranous  labyrinth 332 

150.  Acoustic  epithelium 333 

151.  Canals  of  the  cochlea 334 

152.  Corti's  organ 335 

153.  Tactile  papillae 340 

154.  Pacinian  corpuscles 341 

155.  Olfaotory  bulb       343 

156.  The  tongue 340 

157.  Circumvallate  papillae 347 


THIRD  BOOK  OF  PHYSIOLOGY 


CHAPTEK    I 

0 

A    GENERAL   VIEAV   OF   THE   SUBJECT 

Matter  and  life. — 3Iau  hiis  always  been  interested 
in  the  study  of  his  own  body.  It  is  natural  for  liim  to 
look  about  and  make  comparisons  between  other  objects 
aud  himself.  He  observes  that  every  known  form  of 
matter  is  either  an  inert,  lifeless  substance,  as  stone, 
iron,  water,  and  air,  or  is  organized  and  endowed  with 
life,  as  in  vegetables  and  animals. 

The  great  bulk  of  matter  is  lifeless,  but  the  small  part 
that  is  endowed  with  life  is  of  greatest  interest  and  im- 
portance. 

We  do  not  know  what  life  is,  but  we  do  know  that  it 
has  a  wonderful  influence  upon  matter  that  is  taken  into 
the  bodies  of  plants  and  animals. 

We  know  that  vegetables  and  animals  are  alive  for 
three  reasons  :  (1)  They  can  take  up  lifeless  matter  called 
their  food  and  can  change  it  in  such  a  way  that  it  builds 
up  and  strengthens  their  own  bodies.  Only  a  live  body 
can  do  this.  (2)  They  can  reproduce  their  own  kind. 
They  are  both  made  up  of  small  bodies  called  cells,  and 
the  cells  can  produce  others  just  like  themselves.     The 

6 


G  THIRD   BOOK   OF   PHYSIOLOGY 

cells  of  a  live  body  only  can  do  this.  (3)  They  can  move. 
It  is  true  a  tree  cannot  move  about  bodily,  but  there  is  a 
constant  movement  within  ite  cells,  as  will  be  explained 
in  the  next  chapter. 

Any  body  that  can  do  these  three  things  is  alive. 

Animals  and  vegetables. — Some  minute  organ- 
isms are  of  such  a  low  order  that  it  is  not  possible  to  tell 
whether  they  are  animals  or  plants.  In  all  the  higher 
orders,  however,  there  is  a  clear  distinction  between  the 
animals  and  the  plants. 

(1)  Animals  have  the  power  of  voluntary  motion  of 
the  whole  body,  while  plants  are  fixed  to  one  place. 

(2)  Animals  feed  on  complex  foods  that  have  been 
prepared  by  plants,  while  plants  feed  on  simple  foods, 
such  as  minerals,  water,  and  carbon  dioxide. 

(3)  Animals  have  a  distinct  digestive  tract  within  the 
body,  while  plant  food  is  prepared  in  the  green  leaves. 

(4)  Animals  are  endowed  with  a  distinct  nervous  sys- 
tem, to  which  plants  have  nothing  to  correspond.  Mail 
is  an  Animal. 

Classes  of  animals. — The  animal  kingdom  is  di- 
vided in  modei'n  zoologies  into  twelve  branches.  The 
lowest  branch  includes  the  Protozoa.  This  word  means 
Jirst  life,  and  is  a  general  name  for  a  group  of  the  lowest 
kind  of  animals.  All  these  are  of  very  simple  structure, 
and  so  small  that  they  can  be  seen  only  by  aid  of  the 
microscope.  They  may  be  found  wherever  there  is  water. 
During  their  lifetime  they  are  composed  of  but  a  single 


A  <;RNK^^\L  v.ifw  of  tiik  sriuKcT       7 

cell,  aii.l  yet  they  eat,  breathe,  move,  feel,  and  reproduce 
like  utluT  animals,  oiilv  in  a  verv  simiile  wav. 

From  thest*  lowest  foiins  of  the  animal  kinjjjdom  there 
is  a  gradual  rise  to  higher  and  more  complex  forms. 
Many  cells  unite  to  form  one  lx)dy,  and  different  kinds 
of  cells  form  organs  with  special  functions. 

The  highest  branch  of  the  animal  kingdom  is  the  IV/- 
tebratf's.  This  includes  all  animals  that  have  a  backbone. 
Mtin  is  a  Veiiehrate  AnhnAl. 

The  vertebrates. — Vertebrate  animals  are  of  six 
kinds.  (1)  The  Cyclosiomata.  a  kind  of  eel  without  true 
bones,  and  with  only  a  trace  of  a  backlx)ne.  It  gets  its 
name  from  the  fact  that  its  mouth  is  circular  and  always 
stands  open.  The  lamprey  is  an  example  of  this  class. 
(2)  The  Fishes.  (3)  The  Amphibia,  vertebrates  which 
spend  the  early  part  of  their  life  as  tadpoles  in  water, 
such  as  toads  and  frogs.  (^4;  The  Beptiles.  (5)  The 
Birds.     (6)  The  Mammals. 

Mammals  are  distincruished  bv  the  hair  on  the  IhxIv 
and  by  the  mamumry  gland  that  secretes  milk  for  the 
nourishment  of  their   joung.  They  also  differ  from 

the  other  vertebrates  in  having  a  midriff,  or  diaphragm, 
that  separates  the  chest  from  the  abdomen.  Man  is  a 
Mamma2. 

The  study  of  man. — We  are  about  to  study  the 
wonderful  structure  and  oi)eration  of  the  highest  and 
most  complex  organism  in  wliich  life  resides, — the  hu- 
man bodv. 


8  THIRD   BOOK   OF   PHYSIOLOGY 

.  Scientists  have  investigated  and  experimented  for  many- 
years  to  find  out  how  the  body  is  made  and  how  it  oper- 
ates. While  many  things  are  yet  without  a  satisfactory 
exi^lanation,  much  is  known  with  certainty,  and  with 
these  things  all  should  be  familiar. 

The  more  one  knows  the  more  he  can  do,  and  the 
greater  is  his  pleasure,  whether  he  reads,  travels,  works, 
converses,  or  communes  with  his  own  thoughts. 

The  chief  object  in  this  stud\',  however,  is  that  it  may 
lead  to  the  development  of  a  sound  and  skilful  body. 

Man  is  capable  of  high  development  of  both  mind  and 
body,  but  those  who  are  ignorant  of  the  principles  of 
physiology  and  hygiene  are  apt  to  follow  instincts,  appe- 
tites, and  passions  rather  than  intelligence  and  reason. 
Although  knowledge  alone  will  not  produce  a  sound  body 
or  a  sound  mind,  yet  the  practice  which  should  accom- 
pany knowledge  is  much  more  likely  to  follow  when 
there  is  an  intelligent  basis  for  the  manner  and  purpose 
of  eating,  breathing,  sleei)ing,  working,  and  study. 

A  healthy  body  and  a  vigorous  mind  are,  as  a  rule, 
found  together. 

The  great  advantages  of  good  health  should  furnish  a 
sufficiently  strong  motive  for  understanding  the  condi- 
tions by  which  it  can  be  secured. 

The  three  divisions  of  the  subject.— When  a 
machinist  undertakes  to  operate  a  machine  with  which 
he  is  not  familiar,  he  first  makes  a  study  of  it  and  tries 
to  answer  three  questions  : 

(1)  How  is  it  constructed? 


A    (iFA'F.K'AI.    VIKW    OF   TIM-:    sril.IKC.T  [) 

(2)  What  is  tlic  use  nf  cadi  part,  and  how  (hx'S  it 
()|K'rat('  ? 

(3)  How  can  it  1m'  iiia(h'  !(►  operate  most  enicit'iitly  and 
k(M'})  ill  i;()o(l  runnini;'  order? 

Tilt'  liunian  body  is  a  machine  more  complex  and  intri- 
cate than  anything  the  mind  lias  hoxm  able  to  devise. 
Mduy  of  its  operations  are  automatic,  but  the  whole  body, 
cither  directly  or  indirectly,  is  placed  under  the  control  of 
the  mind  which  resides  within  it.  The  freedom  of  choice 
makes  each  one  responsible  for  his  physical  condition. 

The  three  divisions  of  this  subject  are  : 

(1)  Anatomy,  a  description  of  the  construction  of  the 
body. 

(2)  Physiology,  a  description  of  the  use  and.  operations 
of  the  various  parts  of  the  body. 

(3)  Hygiene,  a  description  of  the  conditions  and  laws 
of  good  health. 

Anatomy. — The  word  anatomy  is  from  two  Greek 
words  which  mean,  to  cut  apart.  The  act  of  cutting  a 
body  apart  to  determine  the  structure  of  its  parts  is  called 
dissection.  What  we  learn  about  the  situation,  structure, 
and  adaptability  of  the  various  parts  of  the  body  is 
called  the  anatomy  of  those  parts.  For  example,  in  giving 
the  anatomy  of  the  stomach  we  would  tell  its  location  in 
the  body,  its  shape  and  size,  its  openings,  its  linings,  and 
its  relation  to  other  organs. 

Physiology. — The  word  physiology  is  made  up  of  two 
Greek  words  which  together  mean,  a  discourse  on  nature. 


10  THIHD   BOOK   OF   PHYSIOLOGY 

The  woi'd  is  now  applied  to  nature  only  as  it  is  seen 
in  animals  and  plants.  In  this  book  we  shall  studj^ 
nature  only  as  it  is  seen  in  man.  The  proper  title  of 
this  book,  then,  is,  The  Physiology  of  the  Human  Body. 

Physiology  proper  deals  only  with  the  activities  of  the 
various  parts  of  the  body.  In  giving  the  physiology  of 
the  stomach,  we  describe  its  movements  and  the  effect 
of  its  secretions  upon  the  food  within  it. 

The  term  is  also  used  in  a  broad  sense  including  both 
anatomy  and  hygiene.  In  this  sense  it  is  used  as  a  title 
of  this  book. 

Hygiene. — The  word  hygiene  is  from  a  Greek  word 
which  means  health.  The  name  of  the  goddess  of  health 
in  mythology  is  Hygeia  Hygiene  treats  of  the  principles 
and  rules  which  have  for  their  object  the  promotion  of 
good  health. 

Aids  to  the  study  of  physiology.— All  the 
sciences  are  very  closely  related,  and  each  one  helps  to 
explain  the  others.  Progress  in  the  study  of  physiology 
has  been  possible  only  in  proportion  as  the  other  great 
sciences  have  advanced. 

The  chemist  can  analyze  the  matter  of  the  body  and 
determine  its  composition.  He  can  also  determine  the 
composition  of  foods  and  their  adaptability  to  the  needs 
of  the  body.  He  can  follow  the  food  in  its  circuit  through 
the  body  and  can  note  the  changes  it  undergoes,  thus  de- 
termining the  chemical  function  of  the  organ  through 
which  it  passes. 


A    GENERAL    VIKW    OF   TlIK   SUIUKCT        11 

Physics  throws  lit;hl  \\\u)\\  Ihc  study  of  i)hysioh>gy  in 
funiisliino-  ;i  cN^nr  know  i<'(lu<.  ,,i"  jj,,.  ukm  li;niic:ii  juiiici- 
pU'S  omi)U)y(Hl  in  the  body,  tlic  ciK'rjry  valiH'  <>{'  foods, 
and  ill  sliowiiio-  Miat  th(5  body  is  a  true  machine. 

^rodorn  biolo.cjy  h;is  been,  probably  more  than  any 
other  science,  n  ,ii:rent  source  of  information  in  re^^ard  to 
living  nature  in  motion.  The  biologist  is  not  satisfied 
with  snperficial  knowledge,  but  searches  for  the  basis  of 
even  life  itself.  The  microscope  has  been  a  powerful  in- 
strument in  his  hands,  and  has  opened  to  his  view  the 
structure  and  activity  of  the  living  cell.  The  subject 
of  physiology  cannot  be  clearly  understood  without  a 
knowledge  of  the  activities  within  the  cell.  For  this 
reason  the  next  chapter  is  devoted  to  a  study  of  the  cell. 


REVIEW  QUESTIONS. 
These  and  similar  sets  of  questions  at  the  end  of  chapters  should 
be  assigned  as  definite  lessons  to  be  carefully  prepared.  The  pupil 
is  not  ready  to  recite  the  review  lesson  until  he  can  answer  each 
question  without  turning  to  the  text.  It  is  a  good  plan  in  this  sub- 
ject, as  in  most  others,  to  insist  on  having  the  first  lessons  very 
thoroughly  prepared  and  understood.  Successful  preparation  of 
the  first  lessons  is  sure  to  result  in  an  interest  in  the  subject  and 
greater  effort  in  the  lessons  that  follow.  Each  succeeding  chapter 
is  written  on  the  assumption  that  the  preceding  one  has  been  mas- 
tered. 

1.  What  are  the  proofs  of  life? 

2.  Is  it  proper    to  use   the  expression  'Mive  coal"    or  ''live 
wire"? 

3.  How  can  you  distinguish  between  animals  and  plants? 

4.  Is  a  dead  ox  an  animal  ?    What  is  it  ? 


12  THIRD   BOOK   OF   PHYSIOLOGY 

5.  "What  is  the  lowest  branch  of  the  animal  kingdom  ?    What 
is  their  manner  of  life? 

6.  What  is  the  highest  branch  ? 

7.  Give  in  order  the  six  kinds  of  vertebrates. 

8.  Give  an  example  of  each  kind. 

9.  "What  does  the  word  amphibia  mean?     (See  dictionary. ) 

10.  Xame  three  things  that  distinguish  mammals. 

11.  How  does  an  animal  differ  from  a  brute? 

12.  What  is  man's  position  in  the  animal  kingdom? 

13.  Of  what  advantage  is  a  knowledge  of  physiology  ? 

14.  Does  a  body  need  to  be  large  in  order  to  be  healthy? 

15.  AVhat  would  you  say  of  a  strong  body  that  was  unskillful? 

16.  What  are  the  three  things  a  machinist  must  know  about  his 
machine  ? 

17.  What  are  the  three  divisions  of  physiology? 

18.  Define  anatomy. 

19.  Define  physiology. 

20.  Define  hygiene. 

21.  In  what  broad  sense  is  the  term  physiology  often  used  ? 

22.  AMiat  other  sciences  aid  in  the  study  of  physiology  ? 

23.  Of  what  use  is  the  microscope  in  this  study? 

24.  W^hat  is  biology  ?     ( See  dictionary. ) 


('II  A  VTKU    n 


THE  ('p:lls  of  the  body 


What  the  cell  is.— ^lost  cells  are  too  small  to  be 
seen  by  the  naked  eye,  but  the  microscope  reveals  not 
only  the  cell,  but  the  minute  parts  of  which  it  is  com- 
posed. Fig.  1  represents  a  cell  which  may  be  taken  as 
a  type  of  all  cells.  On  the  out- 
side  is  the  cell-wall,  which  may 
be  thin  or  thick,  circular  or  ir- 
regular in  shape,  or  may  be  want- 
ing altogether.  The  cell-wall  is 
not  alive,  but  is  the  material 
which  has  been  secreted  by  the 
live  material  within  the  cell. 
Within  the  walls  is  the  cell-sub- 
stance, or  protoplasm.  This  sub- 
stance makes  up  the  most  of  the  cell  and  is  found  alike 
in  cells  of  j^lants  and  animals.  It  is  a  somewhat  trans- 
parent mass,  in  some  cases  a  thin  liquid,  and  in  others 
thick  like  jelly. 

Lying  within  the  protoplasm  is  the  nucleus.  This  is 
a  small  body  surrounded  by  a  membrane  and  having 
within  it  several  smaller  bodies  called  nucleoli.  The 
nucleus  is  an  essential  part  of  the  cell,  as  will  be  shown 
later. 

13 


Fig.  1.— Typical  cell.  C, 
cell-wall  ;  ^V,  nucleus  ;  n, 
nucleolus  ;   P,  protoplasm. 


14 


TIIIED   BOOK   Ot^   PHYSIOLOGY 


Cellular  structures.— AH  living  bodies  are  made 
up  uf  cells.  Some  very  small  animals  consist  of  only- 
one  cell,  but  all  higher  animals 
and  plants  are  composed  of  many 
thousands  of  them.  Plant- cells 
are  usually  enclosed  in  heavy 
walls,  and  when  they  are  crowded 
one  against  another  they  are 
forced  to  assume  a  shaj^e  best 
suited  to  the  space  they  occupy, 
as  shown  in  Fig.  2.  In  Fig.  3 
is  shown  the  arrangement  of  cells 
in  a  twig  of  basswood  as  seen 


Fig.  2. — Diagram  of  a  col- 
lection of  plant-cells. 


Fig.  3. — Microphotograph  uf  a  cro-=s--eciion  of  a  twig  of  basswood. 


through  a  low-power  microscope.      The  outline  of  the 
cell-walls  can  be  plainly  seen  arranged  in  rows  radiating 


Tin:    CIILLS   OF   TIIK    I'.ohV  i:. 

from  the  ce'iitic.  Dry  wood,  in  fact,  is  oiil\  a  collection 
of  cell-walls.  riie  slreii^rth  of  wood  depends  on  the  kind 
and  anioiiiil  of  material  «leposited  in  the  walls  of  the 
cells.  Fig.  4  gives  the  appeanince  of  a  cross-section  of 
pine  wood. 


Fig.  4. — Cross-section  of  pine  wood. 

In  i:)lants  as  in  animals  there  is  a  division  of  work 
among  the  cells.  Some  assume  the  office  of  protection 
of  the  others.  Some  collect  and  prepare  the  plant  food. 
A  great  variety  of  work  is  performed  by  the  various 
tissues  of  which  tlie  plant  is  composed.     Fig.  5  shows 


Fig.  5.— Surface  of  leaf  showing  stomata. 

the  microscopic  appearance  of  the  surface  of  a  leaf. 
The  large  flat  cells  are  plainly  seen,  but  the  points  of 
chief  interest  are  the  modified  cells  about  the  stomata ^  or 


16  THIRD   BOOK    OF   PHYSIOLOGY 

mouths.  These  are  a  good  example  of  special  functions 
of  cells.  Their  office  is  to  regulate  the  transpiration  of 
water  from  the  leaves.  When  water  in  the  leaves  is 
scant,  these  cells  close  the  stoma  and  prevent  its  escape, 
but  when  water  is  present  in  excess  the  cells  open  the 
stoma  and  permit  it  to  freely  evaporate. 

The  cells  of  plants  have  many  characteristics  in  com- 
mon with  those  of  animals,  though  the  latter  are  often 
less  clearly  defined  and  more  difficult 
to  study.  In  the  tissues  of  animals 
a  distinction  should  be  made  between 
the  cell  proper  and  the  material  which 
Fig.  6.— Bone-cells.  ^^^^  cells  collect  about  themselves.  In 
Fig.  6  is  a  representation  of  three 
bone-cells  highly  magnified.  The  spaces  between  the' 
cells  are  filled  in  with  bone  material  which  may  be 
considered  the  walls  of  the  cells. 

In  the  same  way  the  muscle,  nerves,  cartilage,  and 
other  tissues  are  largely  composed  of  material  which  the 
cells  have  built  np  about  themselves  and  which  may  be 
considered  a  cell-wall  modified  to  suit  the  special  pur- 
pose of  the  tissue. 

The  origin  of  cells.— The  body  of  man,  as  well 
as  the  bodies  of  all  higher  animals  and  plants,  begins  as 
a  single  cell,  or  egg.  The  egg,  A,  Fig.  7,  divides  into 
halves  forming  two  complete  cells.  Each  of  the  halves, 
in  turn,  divides  into  two,  making  four,  then  eight,  six- 
teen, thirty-two,  and  so  on.  Several  stages  in  the  divi- 
sion of  the  egg  are  illustrated  in  Fig.  7.     The  last,  U, 


THE    TRLLS    OF    TIIF.    P.oDV 


has  the  appeiirance  of  a  l>eiry,  and  is  Ciilled  the  imilherry 
stage  of  develo])iiient.  This  Imudh'  of  cells  is  closely 
bound  together,  and  continues  to  grow  by  a  multiplica- 

rion  of  cells  and  an  accumulation 
of  cell  material.  The  bodies  of  man 
and  all  higher  animals  are  formed 
out  of  such  bundles  of  cells.  All 
start  as  a  single  cell,  which  by  di- 
viding and  subdividing  results  in 
the  growth  of  the  body.  The  body 
of  a  full-grown  man  is  composed  of 
many  millions  of  cells. 

Parts   of   a   cell. — Microscopes 
have  been  very  much  improved,  and 


Fig.  7. — Diagram  il- 
lustrating the  multipli- 
cation of  cells  from  a 
sintrle  cell. 


Fig.  8. — Appearance  of  a  cell  under  a 
strong  microscope. 


scientists  have  learned  much  better  ways  of  using  them, 
so  that  now  they  can  see  many  things  which  before  es- 
caped their  notice.     In  Fig.  8  is  shown  a  cell  as  it  ap- 


18  THIRD    BOOK    OF   PHYSIOLOGY 

pears  under  a  modern  microscox^e.  The  protoplasm,  F, 
has  the  appearance  of  a  mass  of  foam.  ]S[ear  the  centre 
of  the  cell  is  the  nucleus  surrounded  by  a  membrane,  m. 
Within  the  membrane  appear  two  different  kinds  of  sub- 
stances. One  is  like  the  protoplasm  in  the  body  of  the 
cell,  and  the  other  is  represented  in  the  figure  by  the 
heavy  lines,  ch.  This  latter  substance  is  called  chromatin, 
and  is  one  of  the  most  interesting  and  important  parts 
of  the  cell.  Just  above  the  nucleus  aj)pear  two  aster-like 
bodies,  c  These  are  called  centrosomes.  At  first  only  a 
very  small  dot  appears,  but  soon  it  divides  into  two, 
which  are  later  surrounded  by  the  radiating  fibres  as 
shown. 

The  other  marks  are  not  essential  i)arts  of  the  cell. 
An  empty  space  is  seen  at  v,  and  d  is  only  a  speck  of 
lifeless  matter. 

The  nucleus. — All  cells  have  a  nucleus  in  some 
form.  It  is  the  most  essential  part  of  the  cell.  Without 
the  nucleus  a  cell  cannot  assimilate  food  or  reproduce 
itself.  Some  interesting  experiments  have  been  per- 
formed to  demonstrate  the  importance  of  this  part  of  the 
cell.  Certain  small  animals  are  made  of  only  one  cell, 
but  are  large  enough  so  that  they  may  be  cut  into  parts 
and  the  action  of  the  parts  observed  through  a  micro- 
scope. In  Fig.  9  is  a  representation  of  such  an  animal. 
A  bead-like  string  of  nuclei  extends  through  its  body. 
If  it  be  cut  into  parts  as  shown  at  B,  the  two  ux)i)er 
pieces  will  contain  nuclei,  but  the  lowest  one  will  not. 
It  would  then  be  observed  that  the  two  nucleated  pieces 


TiiK  cKi.Ls  or  'rill-:  r.oDv 


i:» 


live  on  as  tliou^'^li  iiothin*:^  liiid  happened  to  them,  and 
each  ill  time  wouUl  take  on  the  sjime  form  as  the  origi- 
nal.    The  otlier  piece  would  be  observed  to  move  abont 


,■#■ 


,.Al!;'!"'/;".;^:^ 


3^- 


.///?'/'/f/^>j?^ 


dCimCi^^cW?p^^, 


? 


^/~< 


m 


B 


Flo.    0. — .1,    protozoa  ;  5,    same  out   into   three  parts,    the 
being   without    nuclei  ;    C,    the    two    nucleated    pieces   regaini 


lowest 
nir   the 


form  of  the  original. 


for  a  short  time,  but  it  would  not  assimilate  food  or 
change  its  form,  and  soon  its  life  would  cease.  Such  ex- 
periments show  that  the  nucleus  is  a  vital  part  of  the  cell. 


How  new  cells  are  formed. — This  is  a  subject  of 
great  importance  in  biology  and  i^hysiology.  We  here 
give  the  ijrincipal  steps  by  which  one  cell  becomes  two. 
The  diagrams  show  only  the  i^art  of  the  cell  to  which 
attention  is  particularly  directed.  A  cell  at  rest  is  repre- 
sented in  Fig.  10.  The  nucleus  is  filled  with  a  net-work 
of  fibres,  and  just  above  it  are  the  two  dots  called  centro- 
somes.    Sometimes  only  one  dot  is  seen,  but  it  soon  divides 


20 


TIIIED    BOOK    OF   PHYSIOLOGY 


into  two.     These  soon  begin  to  change  in  a  very  interest- 
ing \vay. 

The  first  change  noticed  is  in  tlie  nucleus.  Here  the 
fibres  form  into  a  thread  and  then  break  up  into  a  num- 
ber of  pieces  called  cliromoHomes.  The  number  of  chromo- 
somes is  always  the  same  for  animals  of  the  same  species. 
In  this  cell  there  are  four. 


Fig.  10. 


Fig.  11. 


Fig.  12. 


Fig.  13. 


Fig.  14. 


Fig.  15. 


The  next  change  is  seen  in  the  centrosomes.  They 
assume  a  star-like  appearance  and  begin  to  move  from 
each  other,  as  shown  in  Fig.  12.  though  they  are  still  con- 
nected by  fibres  running  from  one  to  the  other. 

The  membrane  about  the  nucleus  now  disappears,  and 
the  centrosomes  continue  to  separate  until  one  is  on  each 
side  of  the  cell  with  the  chromosomes  between  them,  as 
shown  in  Fig.  13. 


TllK    (MOI.I.S    OK  'rilK    lioDV  L>i 

Tlir  ('li:iiin<'  wliicli  iinw  follows  is  iiiosl  woii<l<'iful  of  all. 
Tln'  cliiomosoinos  Splil  Icii^tliwiso  iiiln  f wo  <mju;i1  pints, 
i'oui- of  tliese,  in  this  pailiciilaf  ccli.  iiionc  to  our  cimiI  i(>- 
soiiie  und  foiii-  lo  111*' ol  her.  The  <li\  ision  of  I  he,  clii-oino- 
soiiies  into  iMiual  parts  insures  tha-t  the  new  eell  will  lu* 
just  like  its  parent. 

Tlie  last  step  in  the  division  is  represented  in  Fi<;.  j5. 
A  partition  grows  thi-ough  the  body  of  the  cell  dividin*^ 
it  into  two  parts.  A  ni(*nibrane  suriounds  each  set  of 
chromosomes,  which  now  become  the  nuclei  of  the  \u)w 
cells.  A  centrosome  remains  with  each  nucleus.  Th(^ 
cells  separate,  and  each  takes  up  its  i^articular  woik  in 
the  body  until  again  they  undertake  the  process  of 
division  just  described. 

The  single  cell. — Manj^  very  small  animals  are  com- 
posed of  only  one  cell.  When  they  divide  and  become 
two,  each  lives  independent  of  the  other.  The  amoeba^ 
shown  in  Fig.  16,  is  such  an  animal.  When  at  rest  it 
may  be  sj^herical  in  form,  and  is  then  only  about  y^Vo  ^^ 
an  inch  in  diameter  and  looks  like  a  lump  of  clear  jelly. 
It  contains  a  nucleus,  but  the  parts  of  its  body  are  all 
alike.  It  has  no  feet,  mouth,  stomach,  or  lungs,  and  yet 
it  moves,  eats,  digests  its  food,  and  breathes.  It  can  i)ut 
forth  a  projection  from  its  body  on  any  side  and  then 
cause  the  rest  of  the  body  to  flow  into  it.  In  that  way  it 
moves  about.  It  may  wrap  its  body  about  other  very 
small  animals  or  i^articles  of  food,  and  digest  them.  In 
that  way  its  whole  body  becomes,  for  a  time,  a  stomach. 
At  any  point  of   its  body  it  takes  in  oxygen  from  the 


22 


THIRD   BOOK   OF   PHYSIOLOGY 


air  in  water  and  gives  out  carbon  dioxide  just  as  other 
animals  do.     Thus  it  can  turn  any  part  of  its  body  to  a 

B 


EiG.  16. — The  amoeba  radiosa.  A,  B.  C,  and  D  are  views  of  the 
same  amoeba,  showing  how  it  changed  its  shape  within  a  few  minutes. 
One  of  the  circles  within  the  body  represents  the  nucleus  and  the  other 
two  are  particles  of  food 
shown  in  this  cut. 


The  amoeba  itself  is  only  3!^  as  large  as 


variety  of  uses,  but  no  one  part  has  any  special  duty  to 
perform. 


THE    ("RLLS   OF   TlIK    IU)I)Y  2:{ 

A  k\u)\v\i'{h^v  of  tlie  jimoeba  is  important  in  a  study  of 
])]iysiolo«iy,  because  a  <j^reat  nunilxT  of  one-eel  led  struc- 
tures of  this  kind  are  found  within  llie  liuniini  body. 
Tliey  are  called  irJiitr  corpx-sclrs,  and  are  of  llu^  <;reatest 
service  to  the  body,  as  will  later  be  shown. 

A  collection  of  cells. — It  is  jdain  that  an  animal 
of  only  one  cell  can  never  grow  very  lar<:;e  oi*  accom]>lish 
very  much  alone.  In  all  liiiiher  animals,  including  man, 
a  great  number  of  cells  are  joined  together  forming  one 
bodj^,  and  the  work  of  the  body  is  divided  among  them. 
Some  cells  are  concerned  only  in  building  up  a  bony 
framework  for  the  body  ;  some  secrete  fluids  needed  for 
the  digestion  of  food  ;  some  form  the  protecting  layer  on 
the  outside  of  the  l^ody.  Just  as  in  a  large  factory  there 
is  a  division  of  labor,  and  each  workman  is  an  expert  in 
some  i)articular  process  or  operation,  so  there  is  a  di- 
vision of  labor  among  the  cells  of  the  body.  Thus  each 
cell  becomes  specially  fitted  for  doing  some  particular 
thing  necessary  to  the  welfare  of  the  whole  body. 

Tissue. — A  number  of  cells  of  similar  origin  grouped 
together  and  having  a  special  work  to  do  in  any  part  of 
the  body  constitute  a  tissue. 

Each  cell  is  alive  and  to  some  extent  is  independent 
of  the  other  cells,  but,  as  already  shown,  a  single  cell  is 
so  small  that  it  is  a  very  helpless  creature  when  alone. 
We  have  to  use  a  good  microscope  to  even  see  it.  A 
single  cell  of  muscle  can  contract,  but  its  etfort  is  very 
feeble.     When^  however,  thousands  of  them  act  together, 


24 


THIJRD   BOOK   OF   PHYSIOLOGY 


the  bundle  of  muscle  is  able  to  lift  beavy  weights  and 
perform  hard  labor. 

There  are  in  the  body  six  different  kinds  of  tissue  : 
(1)  Epithelium  5  (2)  Connective  ;  (3)  Adipose  ;  (4)  Os- 
seous ;  (5)  Muscular  ;  (6)  Nervous. 


Epithelium. — Epithelium  is  the  name  of  the  layers 
of  cells  that  cover  the  whole  outside  of  the  body  and  line 
all  the  vessels  within  that  communicate  with  the  outside. 

Epithelium  is  a  very  common  and  a  \'ery  important 
tissue. 


Fig.  17. — Pjivement  epithelium.         Fig.  18. — Columnar  epithelium. 

-  Its  chief  use  on  the  surface  of  the  skin  is  to  i^rotect^the 
parts  beneath  it.  Here  the  cells  are  flat,  and  are  fitted  to- 
gether at  their  edges  much  like  the  tile  in  a  pavement, 
and  so  it  is  called  pavement  epithelium^  Fig.  17.  The  nails 
and  hair,  also  the  claws  and  horns  of  animals,  are  made 
of  this  kind  of  tissue. 

Another  kind  is  called  columnar  epithelium,  for,  as  seen 
in  Fig.  18,  the  cells  are  set  on  end  and  have  the  appear- 
ance of  columns.  This  kind  of  bells  lines  the  stomach  and 
intestines. 

Still  another  kind,  shown  in  Fig.  19,  is  called  ciliated 
epithelium  because  the  cells  have  projections  at  the  top 


TIIK   (TJ.LS   or   TIIR    r.oDV 


25 


that  look  like  eyelnslies  (ciliaj.     Wliile  the  cells  are  alive 
tlu'  cilia  ;in'  in  coiistnnt  motion.  iMshini:-  back  and  forth. 


Fig.  19. — Ciliated  epithelium. 

Snch  cells  line  the  air-x^assage  of  the  nose,  windpipe,  and 
lungs.  They  are  also  found  in  various  other  parts  of  the 
bodv. 


Connective  tissue. — Connective  tissue  is  distrib- 
uted throughout  the  body,  and  its  duty  is  to  bind  to- 
gether and  sui)port  the  various  parts. 

One  kind  is  called  white  fibrous  tissue.  It  forms  the 
ligaments  which  bind  the  bones  together  at  the  joints. 
It  is  the  tissue  of  the  tendons  that  connect  muscle  to  bone. 
It  serves  as  a  tough  membrane  to  cover  various  organs  of 
the  body.  In  nearly  every  organ  of  the  body  it  is  an  in- 
dispensable connecting  tissue.  When  seen  under  the 
microscope  it  has  the  appearance  of  silvery  white  waving 
bands.  It  is  not  elastic,  but  is  very  strong.  Even  the 
bone  to  which  it  is  attached  will  break  before  the  white 
tissue  will  give  way. 

An  example  of  its  strength  may  be  seen  in  a  butcher- 


2G  THTKD   BOOK    OF   PHYSIOLOGY 

shoj)  where  a  beef  or  pork  is  hung  from  a  peg  by  the  ten- 
don of  the  hind  leg. 

Another  kind  of  connective  tissue  is  called  the  yellow 
elastic  tissue.  It  differs  from  the  white  fibrous  tissue  in 
color  and  also  in  the  fact  that  it  is  elastic.  It  can  be 
stretched,  and  will  return  to  its  original  condition  as  soon 
as  the  stretching  force  is  removed.  It  is  found  in  various 
places  in  the  body  where  such  a  tissue  is  needed,  as  in  the 
skin,  vocal  cords,  and  arteries. 

A  third  kind  is  called  areolar  tissue  because  its  fibres 
are  lax  and  the  spaces  between  them  may  be  easily  filled 
up  with  air  or  a  liquid.  This  tissue  is  very  abundant  in 
the  body.  It  binds  parts  together,  but  allows  them  to 
move  freely  on  each  other.  It  is  found,  for  example, 
just  under  the  skin,  all  over  the  body.  It  is  this  tissue 
which  allows  the  skin  to  have  such  great  freedom  of 
movement.  When  the  hide  is  removed  from  a  dead  ox 
it  is  only  the  areolar  tissue  that  needs  to  be  severed. 

Adipose  tissue. — -Adipose  tissue  is  a  collection  of 
cells  that  contain  fat.  Each  cell  has  a  nucleus  and  is 
alive  like  other  cells,  but  is  degenerate  and  soon  to  die. 
This  tissue  is  found  in  many  parts  of  the  body  within  the 
areolar  tissue.  It  is  often  abundant  beneath  the  skin 
and  around  the  heart  and  kidneys.  The  fat  of  the  cell  is 
a  liquid  while  the  animal  is  alive  but  becomes  solid  after 
death.  Lard  is  obtained  from  the  adipose  tissue  of  the 
hog,  and  tallow  from  that  of  beef. 

Fat  is  also  found  in  the  body  outside  of  adipose  tissue. 
It  is  not  part  of  a  cell,  but  consists  of  little  globules  of 


TIIR    CELLS    OF   TIIK    liohV  27 

fjit  sueli  as  are  roniul  in  tlio  blood.     The  usa  of  Hit  will  \hi 
ih'scvihoi]  under  llu'  subject  of  food. 

Osseous  tissue.  -^>^w'>"s'  fi-ssnf  is  the  name  ai)|)li«'d 
to  tlu^  collection  of  cells  thai  bnild  np  llie  l)one  of  Ihii 
body.  Three  such  cells  are  shown  in  Fig.  0.  Their 
function  is  to  j»ather  from  the  blood  the  material  they 
need,  and  to  Imild  up  around  themselves  the  hard  and 
strong  substance  called  bene.  Bone  is  made  hard  by  the 
lime  compounds — calcium  phosphate  and  calcium  car- 
bonate— which  the  cells  secrete. 

In  some  parts  of  the  body  these  cells  do  not  secrete 
lime,  and  then  the  tissue  is  called  cartilage.  Such  is  the 
nature  of  the  pads  between  bones  at  the  joints,  and  many 
other  parts  of  the  body.  If  the  cartilage  of  the  external 
ear  were  as  inflexible  as  bcme,  there  would  be  great  danger 
that  it  might  be  broken  off  by  accident.  Cartilage,  how- 
ever, is  classed  with  the  osseous  tissue. 

Muscular  tissue. — Muscular  tissue  is  the  name  of  a 
very  abundant  collection  of  cells  which  form  a  material 
called  muscle.  This  tissue  can  contract  under  the  in- 
fluence of  the  cell.  It  thus  pulls  upon  the  bodies  to 
which  its  ends  are  attached  and  draws  the  bodies  closer 
together.  This  tissue  is  used  in  every  motion  that  is 
made  by  the  body. 

Nervous  tissue. — Nervous  tissue  is  a  collection  of 
cells  that  form  the  brain,  the  spinal  cord,  the  nerves,  and 
the  ganglia.     These  cells  are  provided  with  long  thread- 


2S  THIRD   BOOK   OF   PHYSIOLOGY 

like  projections  that  run  out  to  the  cells  of  other  tissues. 
In  this  way  the  nerve-cells  have  a  directing  and  controll- 
ing influence  over  all  parts  of  the  body. 

Organs. — A  collection  of  cells  having  similar  work 
to  perform  is  called  a  tissue. 

A  collection  of  several  kinds  of  tissue  all  working  to 
the  same  purpose  is  called  an  organ.  The  ear,  for  ex- 
ample, is  made  up  of  manj^  different  tissues,  which  to- 
gether form  the  organ  of  hearing.  The  lungs  are  the 
organs  of  respiration.  The  stomach,  intestines,  liver, 
and  pancreas  are  organs  of  digestion.  The  eye  is  the 
organ  of  sight,  and  the  brain  of  thought. 

Systems. — A  system  includes  several  organs  working 
together  to  the  same  end.  The  circulatory  system  would 
include  all  organs  that  have  to  do  with  the  circulation 
of  blood  or  other  fluids.  These  would  be  the  heart,  arte- 
ries, capillaries,  veins,  and  lymphatics. 

Six  important  systems  may  be  named  :  digestive^  circula- 
tory, respiratory,  nervous,  excretory,  and  motor. 

The  excretory  system  includes  all  those  organs  that  are 
concerned  in  getting  rid  of  the  waste  products  or  other 
substances  that  would  be  injurious  if  retained  in  the 
body. 

The  motor  system  includes  the  muscles,  bones,  ten- 
dons, and  motor  nerves  as  far  as  they  are  concerned  in 
giving  to  the  body  its  variety  of  motions. 

Many  organs  belong  to  two  or  more  systems.  The 
lungs,  for  example,  are  organs  of  respiration,  but  in  ex- 


Tin:    CKLLS    OF   TJIK    HuDY 


29 


piralioii  tlicy  an'  also  oriians  of  excretion,  sinee  earlxm 
dioxide  and  otlier  waste  matter  thus  escape  into  the  air. 


Glands. — In  many  i)laces  in  the  body  it  is  necessary 
to  secrete  Irom  the  blood  certain  liqnids  wbicli  are  needed 
in  the  economy  of  the  body.  Examples  of  such  secre- 
tions are  the  juices  needed  to  digest  food,  and  the  sweat 
which  is  poured  out  on  the  skin. 

At  otlier  places  it  is  necessary  to  excrete  matter  for 
which  the  body  no  longer  has  any  need,  or  matter  which 
would  be  harmful  if  not  j^romptly  thrown  off.  An  ex- 
ample of  this  is  the  urea  which  is  excreted  by  the 
kidneys. 

Secretion  and  excretion  are  accomplished  by  organs 
called  glands.  A  simple  form  of  gland  is  represented  in 
Fig.  20.  It  consists  of  a  layer  of  epi- 
thelial cells  built  U2^  in  connective 
tissue  around  a  cavity  and  having  an 
outlet  called  a  duct.  A  net-work  of 
blood  capillaries  lies  close  to  these  cells 
on  the  outside.  The  cells  take  from 
the  blood  the  material  suited  to  the 
special  purpose  of  the  gland.  For 
example,  the  glands  of  the  mouth  will 
secrete  saliva  and  those  in  the  stom- 
ach will  secrete  gastric  juice. 


Fig.  20.— Type  of 
gland.  C,  cavity 
surrounded  with  epi- 
thelial cells ;  d,  duct. 


Serous  and  mucous  membranes.— The  two 
principal  lining  membranes  of  the  cavities  of  the  body 
are  the  serous  and  mucous  membranes.     The  serous  mem- 


30  THIED    BOOK    OF   PHYSIOLOGY 

brane  lines  all  cavities  that  are  closed,  that  is,  having 
no  communication  with  the  outside  of  the  body.  This 
membrane  lines  the  cavities  of  the  abdomen,  and  is  there 
called  the  peritoneum  ;  it  covers  the  lungs,  and  is  there 
called  the  pleura  ;  it  surrounds  the  heart,  and  is  there 
known  as  the  pericardium. 

Serous  membrane  is  thin  and  glistening  and  always 
moist  in  a  healthy  body.  It  is  a  protection  and  support 
to  the  body  it  surrounds. 

The  mucous  membraiie  lines  all  cavities  that  communi- 
cate with  the  outside. 

It  may  be  considered  as  a  continuation  of  the  skin 
which  covers  the  outer  surface  of  the  body.  It  is  com- 
posed of  layers  of  epithelial  cells,  and  contains,  in  many 
places,  small  glands  which  secrete  fluids  suited  to  the 
purpose  of  the  organ  which  they  line. 

The  two  cavities  of  the  trunk. — The  trunk  of 
the  body  is  divided  into  two  main  cavities.  The  upper 
one  is  called  the  thorax  and  the  lower  one  the  abdomen. 
They  are  separated  by  the  diaphragm,  which  is  a  parti- 
tion between  them.  The  lungs,  heart,  and  large  blood- 
vessels are  the  principal  organs  in  the  thorax. 

In  the  abdomen  are  the  stomach,  small  and  large  in- 
testines, liver,  kidneys,  spleen,  pancreas,  and  numerous 
blood-vessels. 


THE   CELLS   OF   THE    BODY  31 

QUESTIONS   FOR   REVIEW. 

1.  What  lire  f(»ur  i)arts  of  a  typical  c«'H  ? 

2.  What  is  protoplasm  ?   (Consult  also  the  dictionary  and  cyclo- 
pa'dia. ) 

3.  What  is  wood? 

4.  What  are  stoniata,  and  how  d(j  they  operate? 

5.  What  distinction  is  made  between  the  cell  and  the  cell  mate- 
rial ? 

6.  Make  a  drawing  of  seve/al  bone-cells, 

7.  How  do  cells  originate? 

8.  What  is  the  unit  in  the  animal  body? 

9.  Make  a  drawing  to  illustrate  the  appearance  of  a  cell  under 
a  strong  microscope. 

10.  l)escribe  the  several  parts  that  may  be  yeen. 

11.  Describe   an   experiment    showing    the   importance   of    the 
nucleus. 

12.  Describe  six  steps  in  the  formation  of   new  cells  from  old 
ones. 

13.  What  is  karyokinesis  ?     (See  dictionary. ) 

14.  What  part  of  the  process  makes  it  almost  certain  that  the 
new  cells  will  be  like  the  old? 

15.  Describe  the  amteba. 

16.  How  is  it  different  from  other  animals? 

17.  What  cells  of  similar  kind  are  in  the  body? 

18.  What  is  meant  by  a  division  of  labor? 

19.  What  is  the  advantage  of  a  collection  of  cells  ? 

20.  What  is  a  tissue  ? 

21.  How  many  kinds  of  tissue  in  the  body?     Name  them. 

22.  Define  epithelium. 

23.  Describe  and  make   drawings   of    three  different  kinds  of 
epithelium. 

24.  Why  should  there  be  different  kinds?, 

25.  What  is  the  function  of  connective  tissue  ? 


32  THIRD    BOOK    OF   PHYSIOLOGY 

20.  Describe  and  give  examples  of   three  kinds  of   connective 
tissue. 

27.  Describe  adipose  tissue. 

28.  What  is  osseous  tissue  ? 

29.  What  is  the  function  of  muscular  tissue  ? 

30.  What  is  the  relation  between  the  nervous  tissue  and  the 
other  tissues  ? 

31.  What  is  an  organ  ?     Give  examples. 

32.  What  is  a  system  ?     Name  six. 

33.  Define  the  duty  of  each  system. 

34.  What  is  secretion  and  excretion  ? 

35.  Describe  the  structure  of  a  simple  gland. 

36.  Of  what  use  are  glands  ? 

37.  What  is  serous  membrane,  and  where  is  it  found  in  the  body? 

38.  What  kind  of  organs  are  lined  with  mucous  membrane  ? 

39.  What  kind  of  fluids  do  glands  secrete  ? 

40.  What  are  the  two  main  cavities  in  the  trunk  of  the  body, 
and  what  are  the  chief  organs  in  each? 


CnAPTEK    III 
THE   SKELETON 

The  skeleton  of  the  human  body  is  made  of  bonevS, 
with  pa<ls  of  cartilage  at  the  joints  and  strong  ligaments 
holding  the  joints  in  place.' 

Use  of  bones. — Bones  are  of  great  use  to  the  body 
in  four  dififerent  ways.  (1)  They  determine  the  general 
figure  and  shape  of  the  body.  (2)  They  protect  the 
delicate  and  vital  parts.  (3)  They  furnish  support  for 
the  softer  parts.  (4)  Many  of  them  can  be  used  as  levers, 
so  that  the  muscles  can  give  to  the  various  parts  of  the 
body  the  kind  of  motion  best  suited  to  our  needs. 

Number  and  names  of  bones.— In  the  adult 
human  body  there  are  two  hundred  and  six  different 
bones,  with  thirty-nine  different  names. 

(The  common  names  of  bones  are  in  constant  use,  and 
are  a  part  of  the  vocabulary  of  every  intelligent  person. 
For  this  reason  the  student  is  urged  to  make  himself 
familiar  with  the  names  given  below. 

Another  reason  for  committing  these  terms  and  others 
that  follow  is  that  any  science  can  be  clearly  understood 
only  when  the  terms  in  which  it  is  expressed  are  clearly 
defined  in  the  mind  of  the  reader.  The  student  is  ex- 
pected not  onh'  to  give  the   names,  but  to  locate  the 

3  33 


THIRD   BOOK   Ot   PHYSIOLOGSf 


Fig.  21. — The  human  skeleton. 
After  a  study  of  the  following  pages  on  the  skeleton,  the  student 
will  be  expected  to  rapidly  name  all  the  parts  here  shown  without 
reference  to  other  pages. 


THE    SKELETON 


35 


The  skill  1—8  bones.    .    . 


The  face— 14  bones .   .  ^ 


hones  either  by  reference  to  bis  own  body  or  by  reference 
to  the  cut  on  the  oj)posite  page  or  on  a  physiological 
chart.) 

BONKS   OF    THK    HUMAN   SKELETON. 

1  Frontal,  forehead. 

2  Temporal,  temples. 
2  Parietal,  sides  uf  head. 
1  Occipital,  back  of  head. 
1  SpHenoid,  base  of  skull. 

1  Ethmoid,  front  of  skull. 

2  Xasal  bones,  bridge  of  nose. 
2  Malar  hones,  cheek. 
2  Lachrijmal  bones,  at  inner  part  of  the 

orbit  of  the  eye. 
2  Turbinated  bones,  in  nostrils. 

1  Vomer,  between  nostrils. 

2  Palate  bo7ie.^,   in   back   part  of   roof  of 
mouth. 

2  Upper  maxillary,  upper  jaw. 

1  Loner  maxillary,  lower  jaw. 

2  Malleus,  the  hammer. 
2  J)icus.  the  anvil. 
2  Stapes,  the  stirrup. 
7  Cervical  vertebrse,  in  neck. 
12  Dorsal  vertebrse,  in  back. 
5  Lumbar  vcrtehrx,  in  small  of  back. 
1  Sacrum,  at  lower  end  of  vertebral  col- 
umn. 

1  Coccyx,  below  sacrum. 
The  ribs— 24:  bones  ...  12  ribs  on  each  side  of  thorax. 
The  sternum— 1  bone    .    .  breast-bone. 
The  OS  innominatum — 

2  bones the  hip-bones. 


The  ear— 6  bones 


The  vertebral  column 
— 26  bones    .... 


36 


THIRD   BOOK   OF   PHYSIOLOGY 


The  hyoid — 1  bone 


The  upper    limbs — 64 
bones 


The    lower   Hmbn- 
bones .... 


-(50 


.  at  base  of  tongue. 
2  Clavicle,  collar-bone,  at  top  of  chest,  in 

front. 
2     Scapula,      shoulder-blade,     back     of 

shoulder. 
2  Humerus,  arm. 
2  Radius,  forearm,  on  same  side  as  the 

thumb. 
2  Ulna,  forearm,  by  the  side  of  the  radius. 
16  Carpal  bones,  wrist-bones. 
10  Metacarpal  bones,  in  body  of  hand. 
28  Phalanges,  3  in  each,  finger  and  2  in 

each  thumb. 
2  Femur,  thigh-bone  from  hip  to  knee. 
2  Patella,  knee-pan. 
2  Tibia,  shin-bone. 
2  Fibula,  by  shin-bone  on  outer  side. 
14  Tarsal  bones,  ankle-bones. 
10  Metatarsal  bones,  in  the  body  of  foot. 
28  Phalanges,  3  in  each  toe  and  2  in  each 

great  toe. 


Classes  of  bones.  Long  bones.— As  to  their 
structure  and  use,  bones  may  be  classified  as  long,  short, 
Jlat,  and  irregular.  The  Jong  hones  are  the  humerus, 
radius,  ulna,  femur,  tibia,  fibula,  metatarsal  and  meta- 
carpal bones,  the  phalanges,  and  the  clavicle. 

Long  bones  are  not  always  of  great  length.  The  bones 
of  the  fingers  are  short,  and  yet  they  are  classed  with  the 
long  bones.  A  long  bone  may  be  described  as  a  hollow 
cylinder,  having  thick  and  very  compact  bony  tissue  at 
its  middle  but  expanded  at  its  extremities,   where  the 


TUK    SKKLETON 


bone  is  of  a  spongy  cliaiadi  r.     1*^1,^.  22  shows  part  of  a 
long  bone  that  h;is  been  cut  in  t\v«>  lengthwise. 


Fio.  22. — Longitudinal  section  of  upper  end  of  femur.     1,  2,  compact 
bone  ;  3,  cancellated  bone. 

Short  bones. — The  short  bones  are  such  as  those  of 
the  carpus  and  tarsus.  Thej^  are  made  of  spongy  bone, 
and  covered  with  a  thin  crust  of  hard,  compact  bone. 


Flat  bones. — The  flat  bones  are  used  to  protect  other 
parts  of  the  body  and  to  furnish  a  broad  surface  for  the 
attachment  of  muscle.  They  are  made  of  two  plates  of 
hard  bone,  quite  close  together,  with  spongy  bone  be- 
tween. 

The  flat  bones  are  the  frontal,  parietal,  occipital,  nasal, 
lachrymal,  vomer,  scapula,  hip-bones,  sternum,  ribs,  and 
patella. 


38 


THIRD   BOOK   OF   PHYSIOLOGY 


Irregular  bones.— The  irregular  bones  are  so  called 
because  of  their  form.  They  are  all  bones  of  the  skele- 
ton not  included  in  the  other  three  classes.  They  all 
have  a  hard,  bony  shell  on  the  outside  with  spongy  bone 
tissue  within. 

The  cranium. — The  cranium  is  a  strong  bony  box 
which  supports  and  protects  the  most  delicate  and  most 
important  organ  of  the  body, — the  brain.  In  the  cranium 
of  the  adult,  as  shown  in  Fig.  23,  the  flat  bones  are  joined 


Fig.  23. — Cranium. 


edge  to  edge  h\  a  kind  of  joint  called  a  suture.  The 
edires  ""row  into  each  other  and  form  a  solid  union.  The 
cranium  of  the  infant  is  soft  and  easily  distorted,  because 
the  bones  are  not  yet  hardened  with  lime. 

All  the  other  bones  of  the  skull  articulate  with  the 
sphenoid,  which,  like  a  wedge,  holds  them  firmly  to- 
gether. 


TIIH   SKKLKTON 


?,'.) 


The  vertebral  COlunm. — Tho  vertebral  column  is 
coiupusod  of  o.i  vertcbnc  (Latin,  vcrtere,  to  turn)  placed 
one  on  top  of  tlie  otlier.  The  cliaracteristic  parts  of  a 
vertebra  are  the  Vmdj',  several  processes,  and  a  perfora- 
tion just  back  of  the  body.     These  an^  shown  in  Fig.  24. 

..s 


i#^^ 


Fig.  24. — Vei'tebra.     B,  body;    T^  transverse  process  ;  S,  spinous 

process. 

The  vertebrae  are  piled  up  in  the  manner  shown  in 
Fig.  28,  and  serve  as  a  strong  pillar  to  hold  up  the  head 
and  the  trunk  of  the  body.  The  holes  together  form  a 
tube  for  the  protection  of  the  spinal  cord. 


Fig.  2.5. — Atlas. 


The  atlas. — The  topmost  vertebra  is  called  the  atlas, 
because  the  head  rests  upon  it  (see  Atlas  in  dictionary). 


40 


THIRD   BOOK   OF   PHYSIOLOGY 


It  differs  in  shape  from  the  other  vertebrae,  as  may  be 
seen  in  Fig.  25.  It  articulates  with  the  base  of  the  skull, 
and  when  the  head  is  turned  it  turns  with  it. 


Fk;.  2*;.— Axis. 

Axis. — The  rsecond  vertebra  is  called  the  axi.s,  because 
it  forms  a  pivot  uj^on  which  the  atlas  rotates.  The  pecu- 
liaritj^  in  the  shape  of  the  axis  is  the  tooth-like  projection 
called  the  odontoid  process.  The  atlas  fits  over  this  x^ro- 
cess  and  rotates  about  it  when  the  head  is  turned  from 
side  to  side. 


Fig.  27. — Sacrum  and  coccyx. 


Sacrum  and  coccyx. — At  the  lowest  point  of  the 
backbone  is  the  coccyx.     In  early  life  it  consists  of  four 


TIIK    SKFJJ«:T()X 


41 


separate  bones,   but  later  tliey  grow  t<>j;elh<*i-  and   fm m 
one   solid   bone,      ft   is  called  the 
coceyx   because  it  looks  like  the 
beak  of  a  euekoo. 

Just  above  the  coccyx  is  the 
sacrum,  or  sacred  bone.  It  is  so 
called  because  it  was  once  used  in 
sacrifices.  In  early  life  it  is  com- 
posed of  five  separate  bones,  but 
later  they  grow  together. 

The  sacrum  and  coccyx,  to- 
gether with  the  two  large  hip- 
bones, form  a  strong  basin  at  the 
base  of  the  trunk  of  the  body.  It 
is  called  the  jx'his,  l>ecause  lyelvin 
in  the  Latin  language  means  basin 
(see  skeleton  on  page  34). 


Flexibility  of  the  back- 
bone.— The  bod}'  of  each  vertebra 
is  about  one  inch  thick.  AVhen 
they  are  placed  one  on  top  of  the 
other  thay  form  a  cobimn  that  is 
slightly  curved  like  the  letter  S. 
The  bony  i:)art  of  the  vertebraj  do 
not  touch  each  other.  There  is  a 
pad  of  elastic  cartilage  between 
them,  and  all  are  bound  firmlj' 
together  by  strong  ligaments. 

Both  the  shajje  of  the  column  and  the  pads  of  cartilage 


Fig.  28. — Showing  curves 
of  spinal  column. 


42 


THIRD    BOOK   OF   PHYSIOLOGY 


prevent  sudden  jars  from  walking,  jumping,  or  a  slight 
fall.  The  cartilage  also  permits  great  freedom  of  move- 
ment in  all  directions. 

The  ribs. — The  ribs  are  flat,  elastic  l)ones  surround- 
ing the  chest.     They  are  twenty-four  in  number,  twelve 


Fig.  29.— The  ribs. 


on  each  side.  The  u^^per  seven  on  each  side  are  true 
ribs,  and  the  lower  five  are  false  ribs.  All  articulate 
with  the  backbone  by  a  true  joint,  two  to  each  dorsal 
vertebra.  In  the  front  the  seven  true  ribs  are  joined 
to  the  sternum  by  means  of  cartilage.  The  fii^t  three 
false  ribs  are  joined  in  front  to  the  cartilage  of  the 
lowest  ti^ue  rib.  and  the  two  remaining  ones  have  no 
attachment  in  front,  and  so  are  QduW^d  floating  ribs.     The 


THE   SKKLKTON 


4:j 


ribs  do  not  pass  strai^lit  aiouiid  the  chest,  but  are  lower 
ill  front,  and  also  sa^  in  llie  niiddlo.  Tlie  advantage  of 
this  will  be  apparent  when  we  come  to  the  study  of 
breathing. 

The  extremities. — There  are  many  points  of  simi- 
larity  between   the  bones  of  the  arms  and   legs.     The 


tei 


Fig.  30. —  Forearm  and  lower  leg. 

femur  is  the  largest  bone  in  the  body,  and  the  corre- 
sponding bone  in  the  arm  is  the  humerus.  The  tibia  is 
the  next  longest,  and  is  on  the  same  side  as  the  great  toe. 
The  radius  of  the  arm  is  a  corresponding  bone  on  the 
same  side  as  the  thumb.     The  fibula  of  the  leg  has  its 


44  THIRD   BOOK   OF   PHYSIOLOGY 

counterpart  in  the  ulna  of  the  arm.  The  tarsus  is  similar 
to  the  carpus.  The  metatarsus  and  metacarpus  are  much 
alike,  and  both  the  feet  and  the  hands  end  in  phalanges. 

QUESTIONS  FOR  REVIEW. 

1.  Give  four  uses  for  bones. 

2.  How  many  bones  in  the  human  body? 

3.  Give  good  reasons  for  learning  their  names. 

4.  Name  and  locate  the  bones  of  the  skull. 

5.  Point  out  and  name  the  bones  of  the  face. 

6.  Define  the  names  of  the  ear  bones. 

7.  What  are  the  three  classes  of  vertebrae?    Locate  them. 

8.  What  are  the  three  kinds  of  ribs? 

9.  Where  is  the  sternum?    The  os  innominatum?     The  hyoid? 

10.  Name  all  bones  of  the  upper  limbs. 

11.  Name  all  bones  of  the  lower  limbs. 

12.  Name  together  the  corresponding  bones  of  the  arms  and  legs. 

13.  Point   out  on  the  chart  all  the  bones  of   the  body,    giving 
names. 

14.  How  are  bones  classified  as  to  their  structure? 

15.  Define  a  long  hone.     Name  all  the  long  bones. 

16.  AVhat  is  the  structure  of  short  hones?     Oijiat  hones  f 

17.  To  which  of  the  four  classes  do  the  ribs  belong? 

18.  Locate  the  sphenoid. 

19.  How  many  vertebrae  are  there,  and  why  are  they  so  called? 

20.  Which  vertebra  is  called  the  atlas  ?    Why  so  called? 

21.  What  is  the  use  of  the  odontoid  process? 

22.  What  is  the  pelvis  f 

23.  What   provision  is  made  to  relieve  the  brain  from  sudden 
jars  ? 

24.  What  is  the  difference  between  the  true,  the  false,  and  the 
floating  ribs  ? 

25.  How  can  you  tell  which  of  the  two  bones  in  the  forearm  is 
the  radius  ? 


CHAPTEE   IV 

STRUCTURE   AND   NOURISHMENT   OF   BONE 

Strength  of  bones.— Bones  which  are  to  serve  as 
a  framework  of  the  bodies  of  animals  should  be  strong 
and  at  the  same  time  light.  This  condition  is  brought 
about  by  making  all  long  bones  in  the  form  of  tubes,  as 
shown   in   Fig.    22.     A   tube    will    support  much  more 


Fig.  31. — Cross-section  of  a  flat  bone. 

weight  than  the  same  amount  of  material  in  form  of  a 
solid  rod.  This  principle  is  utilized  in  the  use  of  hollow 
iron  pillars  for  the  sujjport  of  buildings  and  in  the 
hollow  stalks  of  grasses  and  grains.  In  the  middle  of 
the  shaft  of  the  long  bone  the  tube  is  smaller,  but  the 
walls  are  thicker  and  almost  as  compact  iis  ivory.  To- 
wards the  ends  the  walls  are  thinner  and  the  shaft 
larger.  The  exi^anded  ends  are  filled  with  spongy  bone 
which  looks  something  like  lattice  work,  and  so  is  called 
cancellous  bony  tissue.  The  strength  and  lightness  of  flat 
bones  are  secured  by  having  two  plates  of  compact  bone 
with  cancellous  tissue  between  them.  The  shai)e  and 
structure  of  a  bone  depend  upon  the  nature  of  its  ser 
vice  to  the  body. 

45 


46  THIED    BOOK    OF   PHYSIOLOGY 

Microscopical  examination   of  bone.— When 

we  look  through  the  inicroscoj^e  at  a  very  thin  slice  of 
bone  it  is  seen  to  have  a  very  definite  and  interesting 
structure  which  can  never  be  seen  with  the  naked  eye. 
Fig.  32  ilhistrates  the  appearance  of  such  a  cross-section. 


r^^:r^iM^^^U:.-^^Q, 


tm. 


..  .J  '   -  :-'-~.^~'-  9- ;. 

Fig.  o2. — Cross-section  of  hone,  highly  magnified. 

The  lioles  at  the  centres  of  the  circles  are  only  about  sk 
of  an  inch  across,  some  being  larger  and  some  smaller. 
These  holes  are  tubes  cut  across.  The  tubes  run  length- 
wise with  the  bone  and  are  called  Haversian  canals,  from 
the  name  of  the  discoverer.  Dr.  Havers.  The  bone-cells 
are  arranged  in  circles  around  the  canals.  Their  loca- 
tion may  be  determined  by  the  black,  irregular  spots 
called  lacunce  where  the  living  cell  resides.  Very  fine 
tubes,  called  canaUculi,  ladiate  from  each  lacunae,  con- 
necting them  one  to  another  and  with  the  central  Haver- 
sian  canal.     Each   canal  with   its  concentric  layers  of 


STRUCTrUK   OK    IloXK  47 

lacnnii'  jukI  caiialiculi  form  a  ll<(rrr.sian  si/shni.      IIi<^ljly 
maunilied  Ixnw cells  arc  I'cprcsciilcii  in  Vi*!;.  <!. 

How  bone  is  nourished,  rin-  hone-cells,  like 
most  cells  of  the  body,  arc  lixcd  to  one  i^lace.  Their 
food  must  be  brought  to  them  or  tliey  will  starve.  The 
bones  that  are  usually  picked  up  for  examination  are  dead 
bones.  They  are  no  more  like  the  live  bone  than  a  dead 
twig  on  the  ground  is  like  a  live  one  on  a  tree.  When  a 
live  bone  is  cut,  blood  will  ooze  from  its  numerous  canals. 
It  is  plain  that  the  blood  here,  as  elsewhere,  is  the  agent 
by  which  food  is  brought  to  the  cells.  All  bones  are  sur- 
rounded by  a  membrane  called  the  periosteiun  (around  the 
bone).  In  this  membrane  are  numerous  blood-vessels 
that  enter  the  bone  in  many  places  and  traverse  the 
Haversian  canals.  The  hollow  bones  are  lined  on  the 
inside  with  a  similar  membrane  called  the  endosieum.  An 
arter}^  enters  the  long  bone  usually  through  a  foramen  at 
about  the  middle  of  the  shaft.  It  distributes  itself  in 
the  endosteum.  From  this  source  the  marrow  which  fills 
the  hollow  of  the  bone  receives  its  nourishment,  and  also 
the  inner  layers  of  bone  are  supplied  with  bone  material 
from  the  same  source. 

Composition  of  bone. — A  chemical  examination 
shows  that  bone  is  composed  of  two  kinds  of  substances 
closely  mixed  together.  One  of  these  is  called  animal 
matter  and  the  other  earthy  ^natter, — about  one-third  of  the 
former  and  two-thirds  of  the  latter.  The  earthy  matter 
may  easily  be  removed  from  bone  by  submersion  for  a 


48  THIHD   BOOK   OF   PHYSIOLOGY 

time  ill  dilute  muriatic  acid.  (See  directions  at  end  of 
this  chapter.)  The  acid  readily  combines  with  the  lime 
compounds,  so  that  in  the  course  of  a  day  only  the  ani- 
mal matter  of  bone  remains  in  place.  This  is  now 
so  flexible  that  it  may  be  tied  into  a  knot,  as  shown 
in  Fig.  33. 

A  piece  of  fresh  bone  i:)ut  into  a  hot  fire  for  an  hour  or 
two  will  lose  all  its  animal  matter,  and  onh^  the  hard 
part,  which  is  largely  the  phosphate  and  carbonate  of 
lime,  will  remain  un burned. 

The  bones  of  young  children  are  quite  soft,  because 
they  are  composed  of  a  large  proportion  of  animal  matter. 


Fig.  33. — Bone  tied  in  knot. 

As  the  child  grows  older,  more  and  more  lime  is  de- 
posited about  the  cells,  and  so  the  bones  grow  harder  and 
more  brittle.  Ossification  begins  at  the  middle  of  a  bone 
and  extends  out  to  the  joints. 

The  shafts  of  the  long  bones  are  filled  with  a  yellowish 
fatty  substance  called  marrow.  The  cancellous  tissue  is 
filled  in  with  a  thin  reddish  liquid,  which  is  sometimes 
called  marrow,  though  it  contains  very  little  fat,  while 
true  marrow  contains  96  per  cent.  fat. 

This  red  liquid  is  intimately  connected  with  the  for 
mation  of  new  red  blood-corpuscles. 

Health  of  bone. — Bone  has  but  few  nerves  distrib- 
uted to  it,  and  so  we  feel  but  little  pain  from  any  wound 


STRUCT UEE   OF   BONE  49 

which  it  receives.  It  iiuiy  Imm-oiho  diseased,  however, 
just  like  any  other  part  of  the  body.  (Jood  bone  can  be 
built  up  by  the  cells  only  when  the  necessary  material  is 
furnished  to  them  in  the  blood.  Bone  is  formed  fiom 
the  materials  in  the  food  which  we  eat. 

There  is  a  disease  called  rickets^  which  is  common 
with  children  who  live  on  scant  and  poor  food.  The 
backbone  and  legs  are  often  bent  and  distorted,  because 
the  bone-cells  are  poorly^  fed  and  do  not  build  up  a 
sufficiently  rigid  tissue. 

A  man  does  not  leach  his  full  height  until  about  the 
age  of  twenty-five  years  ;  and,  although  the  bones  may 
have  been  perfectly  healthy,  yet  they  have  been  soft  and 
flexible.  The  hardening  of  bone  continues  even  long 
after  full  growth  has  been  attained.  The  bones  of  chil- 
dren may  be  made  to  take  on  a  variety  of  shapes  and 
positions  which,  if  allowed  to  remain  so,  will  become 
fixed  in  later  life. 

Bow-legs  are  quite  a  common  misfortune,  but  in  most 
cases  the  deformity  could  have  been  prevented  by  proper 
care  in  the  early  life  of  the  child,  or  by  proper  appliances 
while  the  bone  was  still  soft. 

Stoojjing  shoulders  and  a  contracted  chest  are  a  result 
of  careless  habits  of  posture  w^hile  the  bones  are  soft. 
The  fault  cannot  be  corrected  in  later  life.  The  head 
should  be  carried  erect  (not  thrown  back),  the  chest  ex- 
panded forward,  and  the  proper  curve  of  the  backbone 
maintained. 

Tight  shoes  deform  the  bones  of  the  feet,  produce  an 


50  THIRD   BOOK   OF   PHYSIOLOGY 

awkward  and  unsteady  gait,  and  make  walking  a  painful 
exercise. 

A  firm  and  graceful  walk  is  much  more  to  be  admired 
than  a  small  shoe. 

Tight  clothing  about  the  waist  is  sure  to  deform  and 
displace  the  lower  ribs.  The  vital  organs  within  the 
chest  and  abdomen  are  seriously  hindered  in  their  work 
by  such  compression. 

Those  who  sit  long  in  one  place  should  be  careful  of 
their  posture.  School  seats  should  be  of  such  a  height 
that  the  feet  of  the  pupils  may  rest  squarely  on  the  floor. 

Older  pupils  should  have  desks  of  such  size  that  they 
are  never  forced  into  a  cramped  i:)Osition.  All  desks 
should  be  close  enough  together  to  permit  pupils  to  sit 
up  while  they  write  or  do  other  desk  work. 

Fracture  of  bone. — A  broken  bone  is  said  to  be 
fractured;  (1)  when  it  is  a  clean  break  it  is  called  a  sim^Ze 
fracture  ;  (2)  when  the  soft  parts  about  a  break  are  lace- 
rated, so  that  there  is  an  opening  from  the  skin  into  the 
bone,  it  is  called  a  comjwund  fracture. 

It  is  a  wise  provision  of  nature  that  the  bones  of  the 
young  are  soft  and  flexible  5  otherwise,  the  numerous 
bumps  and  falls  to  which  a  child  is  liable  would  be  ac- 
companied by  serious  results.  As  the  child  grows  older 
he  becomes  more  skilful  in  his  movements,  and  learns 
how  to  avoid  accidents.  The  bones  become  harder  and 
stronger,  but  also  more  liable  to  fracture. 

When  bone  is  broken  nature  sets  about  at  once  to  heal 
the  fracture.     At  first  a  watery  fluid  is  poured  out  around 


STKUCTTRK   or    I'.oXE  51 

the  broken  ends,  and  lliis  in  course  of  a  fow  days  will 
heconir  tiiick  like  jcllx .  In  t  liis  a  <leposit  of  lime  is  made 
until  it  is  almost  as  liaid  as  hone  its<'lf.  Thus  a  natural 
splint  is  formed  about  tiie  fracture,  and  the  ends  of  the 
bones  are  hold  more  firmly  in  place.  It  requires  five  or 
six  weeks  for  healthy  bone  to  unite,  and  several  months 
may  elapse  before  union  is  complete. 

It  sometimes  happens  that  bones  will  not  readily  unite. 
This  is  called  iMayed  union.  The  delay  may  be  for 
months,  or  may  even  be  permanent. 

If  the  parts  of  a  broken  bone  remain  in  their  proper  place^ 
and  are  kept  quiet  for  five  or  six  weeks,  nature  alone  will 
repair  the  fracture  in  a  very  satisfactory  manner.  In 
nearly  all  cases,  however,  a  broken  bone  is  also  displaced, 
and  in  that  position  will  not  unite  at  all,  or,  if  it  does, 
will  be  weak  and  crooked. 

For  these  reasons  the  services  of  a  surgeon  should 
always  be  secured  at  once. 

QUESTIONS   FOR  REVIEW. 

1.  How  are  bones  made  both  strong  and  light? 

2.  How  is  this  principle  utilized  in  nature  and  architecture? 

3.  What  determines  the  shape  and  character  of  a  bone?     Give 
examples. 

4.  What  is  a  Haversian  canal?     How  large  are  they?     What  is 
their  use  ? 

5.  What  are  lacuruc,  and  how  are  they  connected  ? 

6.  Where  are  the  bone-cells? 

7.  What  constitutes  a  Haversian  system? 

8.  How  do  bone-cells  get  their  food? 

9.  What  is  the  periosteum  f    The  endosteum  ? 
10.  What  is  inside  the  long  bones? 


52  THIRD    BOOK    OF   PHYSIOLOGY 

11.  What  is  the  composition  of  bone? 

12.  AVhat  kind  of  substance  fills  the  spaces  of  the  cancellous 
tissue  ? 

13.  What  is  the  cause  of  rickets? 

14.  Why  should  young  people  be  careful  of  their  posture  in  sit- 
ting and  walking? 

15.  What  is  the  jjroper  posture  ? 

16.  What  deformities  are  caused  by  tight  clothing? 

17.  What  is  a  simple  fracture  f     A  compound  fractured 

18.  How  are  flexible  bones  an  advantage  to  children  ? 

19.  How  does  nature  try  to  repair  a  fracture? 

20.  Why  is  a  surgeon  needed  when  a  bone  is  broken? 

21.  Why  is  a  horse  usually  shot  when  one  of  his  legs  is  broken? 

EXPERIMENTS. 

Animal  matter  in  bone.— Secure  from  the  butcher  a  clean  fresli  rib  of 
a  lamb  or  sheep.  Place  it  in  a  bottle  or  dish  of  such  shape  that  the  bone  mas- 
be  completely  covered  with  about  one  pint  of  water.  Pour  into  the  water  alx»ut 
three  ounces  of  hydrochloric  acid  and  set  it  aside  for  twelve  hours  or  more.  The 
acid  will  dissolve  the  lime,  leaving  only  the  animal  matter,  which  is  now  so 
soft  and  pliable  it  can  be  tied  into  a  knot. 

Earthy  matter  in  bone.— Place  a  piece  of  fresh  bone  in  the  hot  coals  of 
a  stove  or  furnace  for  two  or  three  hours.  The  animal  matter  will  all  burn 
away,  leaving  only  the  mineral  matter,  which  may  now  be  broken  with  a 
hammer. 

Weigh  the  bone  Ijefore  and  after  burning.  The  difference  in  weight  is  the 
weight  of  the  animal  matter  burned  away. 

Examination  of  a  bone.— Secure  a  fresh  bone  of  the  lower  leg  of  a 
sheep  or  beef  and  make  the  following  observations : 

1.  The  smooth  cartilage  at  the  ends. 

2.  Try  the  strength  of  it. 

3.  Peel  off  some  of  the  periosteum. 

4.  Look  for  au  opening  in  the  side  of  the  bone. 

5.  Saw  the  bone  in  two  lengthwise  and  note  the  thickness  of  the  bony  walls. 

6.  Examine  the  marrow. 

7.  Look  for  cancellous  tissue. 

8.  Find  the  endostemn. 

9.  Secure  any  bone  that  is  not  a  lon^  bone,  saw  it  iu  two,  and  closely  examine. 


CHAPTER     V 


JOINTS 


Use  of  joints. — A  stone  pillar  which  has  been 
chiselled  into  the  likeness  of  a  man  has  no  need  of  joints, 
for  it  will  not  need  to  change  its  position. 

A  tree  needs  no  joints,  for  it  is  by  nature  stationary. 
Joints  would  be  a  source  of  weakness  to  a  tree. 

Man  and  all  the  higher  animals,  however,  must  be 
capable  of  a  great  variety  of  motions  and  movements, 
and  for  that  purpose  they  are  supplied  with  numerous 
joints.  When  a  man  loses  the  use  of  a  single  important 
joint  he  is  at  a  disadvantage  in  the  activities  of  the 
world,  and  is  considered  a  cripple. 

The  structure  of  joints. — In  all  joints  of  the 
body  where  one  bone  glides  on  another,  three  important 
provisions  are  made.  (1)  The  surfaces  are  made  smooth. 
(2)  A  lubricating  fluid  is  supplied  as  needed.  (3)  The 
bones  are  bound  firmly  in  place. 

These  are  just  the  conditions  we  try  to  secure  in  the 
machines  which  we  build,  wherever  one  jyart  must  bear 
uj^on  another  while  in  motion,  and  where  friction  is  to 
be  avoided. 

Articular  cartilage. — The  smooth  surface  of  joints 
is  secured  by  a  layer  of  cartilage  on  the  articulating 


54  THIED   BOOK   OF   PHYSIOLOGY 

ends  of  bones.     This  is  the  only  part  of  a  bone  that  is 
not  covered  with  periosteum. 

The  smoothness  of  the  cartilage  affords  ease  of  move- 
ment and  its  elasticity  helps  to  break  the  force  of  any 
concussion.  The  cartilage  varies  greatly  in  thickness, 
being  thickest  at  points  where  the  greatest  pressure  is 
received, — the  middle  of  the  convex  surfaces  and  the 
edges  of  concave  surfaces. 

Synovia. — The  joint,  however,  would  soon  become 
stiff  or  could  be  moved  only  with  great  difficulty  with- 
out a  lubricating  fluid  ready  at  any  time  it  is  needed. 
Such  a  fluid  is  supplied  to  all  the  movable  joints.  It  is 
called  the  synovial  fluid  because  of  its  likeness  to  the 
white  of  an  e^gg  (see  the  word  in  the  dictionary).  The 
fluid  is  secreted  by  the  synovial  membrane  and  poured 
out  on  the  joint. 

How  joints  are  held  in  place. — The  ends  of  bones 
at  a  joint  must  be  held  to  their  proper  places,  and  at  the 
same  time  there  must  be  freedom  of  movement.  These 
conditions  are  secured  in  a  variety  of  ways.  Strong  liga- 
ments consisting  mainly  of  bundles  of  white  fibrous  tissue 
(see  page  25)  are  fastened  to  the  bones  aboA^e  and  below 
the  joint.  The  hip-joint,  for  example,  is  enclosed  by  a 
set  of  ligaments  which  form  a  capsule  or  box  about  the 
joint.  Such  ligaments  are  very  strong,  and  will  resist 
even  violent  attempts  to  pull  the  joint  apart. 

Air-pressure  also  helps  to  keep  some  of  our  joints  in 
place.     This  is  particularly  true  of  such  joints  as  that  in 


.TOTNTS 


55 


the  liip,  where  the  ball  of  llir  rnnni-  fits  into  the  deep 
socket  of  tlie  lii{»-l)OTie.  Any  attempt  to  laill  tlie  ])all 
from  its  socket  would  Im*  lesisted  by  the  pressure  of  the 
air  because  of  the  vacuum  produci-d  in  the  socket.  Since 
the  diameter  of  the  socket  is  nearly  two  inches,  the  air- 


FiG.  34. — The  hip-joint.     Capsular  ligaments  stripped  back  to  show 

the  ball  and  socket. 

pressure  which  would  resist  any  attempt  to  suddenly 
pull  the  bones  apart  would  be  about  fifty  pounds. 


Kinds  of  joints. — Mature  tries  to  make  each  organ 
of  the  body  most  efficient  in  its  particular  kind  of  work. 
We  would  expect  to  find  that  the  joints  in  the  various 
parts  of  the  body  would  be  of  a  kind  best  suited  to  the 
work  which  that  part  of  the  body  has  to  do.  Joints  may 
be  classified  as  immovable  and  movable^  the  latter  being  of 
greatest  interest  and  importance. 


56 


THIRD   BOOK   OF   PHYSIOLOGY 


The  immovable  joints  are  those  where  the  bones  are 
almost  in  direct  contact,  with  only  a  thin  layer  of  con- 
nective tissue  between  them,  and  without  any  motion  of 
one  upon  the  other.  Such  joints  connect  the  bones  of 
the  cranium.  The  bones  of  the  face,  except  the  lower 
jaw,  are  also  bound  together  by  immovable  articulations. 

There  are  three  important  kinds  of  movable  joints, — 
pivot-jomts.  hinge-joints,  and  ball-and-socket  joints. 

The  pivot-joint  permits  only  the  motion  of  rotation.     A 


Fig.  35. — Example  of  pivot-joint.     Atlas  on  axis. 

good  example  is  found  in  the  motion  of  the  atlas  on  the 
axis  when  the  head  is  turned  from  side  to  side.  The 
relation  of  these  two  bones  is  shown  in  Fig.  35.  Across 
the  ring  of  the  atlas  is  a  strong  ligament  which  holds 
the  atlas  in  place  and  yet  permits  it  to  rotate  about  the 
odontoid  process. 

The  hinge-joint  is  common  in  the  human  body  and  in 
the  bodies  of  all  higher  animals.  Onh'  a  forward  and 
backward  motion  in  one  plane  is  permitted  by  a  joint  of 
this  kind.    The  motion  is  like  that  of  a  door   on   its 


JOINTS  :)7 

hinjjfcs.  A  good  example  is  louiid  in  (lie  last  two  joints 
of  the  fingers.  Those  joints  permit  the  fingers  to  be 
closed  and  opened,  l)ul  do  not  admit  of  any  latei-al 
motion.  The  elbow  and  knee  are  also  exami)les  of 
hinge-joints. 

The  haU-and-socket  joint  allows  greater  freedom  of 
movement  than  is  i)0ssible  with  any  other  kind  of  joint. 
The  best  example  of  such  a  joint  is  found  in  the  hip.  l>y 
reference  to  Fig.  34  it  is  j51ain  that,  within  certain  limits, 
the  leg  can  be  moved  in  auy  direction  desired. 

In  the  shoulder,  where  the  humerus  articulates  with 
the  scapula,  is  also  a  joint  of  this  kind.  The  socket  here 
is  not  so  deep  as  that  at  the  hip.  As  a  result  of  the  shal- 
low socket  the  arms  have  a  greater  range  of  motion  than 
the  legs,  but  the  shoulder-joint  is  more  liable  to  dislo- 
cation. 

Another  kind  of  joints,  called  gliding  joints,  may  also 
be  mentioned.  Examples  may  be  found  in  the  bones  of 
the  carpus  and  tarsus,  which  maj^  glide  slightly  upon 
each  other. 

Health  of  joints. — Joints  are  delicate  in  struc- 
ture, and  so  are  liable  to  disorder  unless  they  receive 
proper  care.  A  diseased  condition  of  the  joints,  called 
gout,  is  common  with  those  who  drink  strong  wine  and 
other  alcoholic  liquors.  The  tendency  to  gout  is  also 
often  inherited. 

Another  serious  disease,  often  located  in  joints,  is  rheu- 
matism. It  is  frequently  the  result  of  negligence  in  the 
niattei:  of  clothing  suited  to  changes  in  the  weather.     It 


58  THIED   BOOK    OF   PHYSIOLOGY 

may  be  caused  by  sitting  in  damp  places,  or  by  neglect- 
ing to  cliange  clotliing  after  exposure  to  wet.  Eheuma- 
tism  is  the  cause  of  a  great  deal  of  pain  and  discomfort, 
and  yields  very  slowly  to  any  treatment  now  known. 

Joints  are  liable  to  sprains  and  dislocations.  When 
the  ligaments  about  a  joint  are  torn  or  unduly  stretched, 
the  joint  is  said  to  be  sj) rained.  Even  slight  sprains 
should  receive  immediate  attention,  for  neglect  may,  as 
has  often  been  the  case,  result  in  stiff  joints. 

When  the  bones  of  a  joint  are  forced  out  of  place  it  is 
called  a  dislocation.  When  this  occurs,  no  time  should 
be  lost  in  calling  a  surgeon  to  put  the  bones  in  place  again. 

QUESTIONS   FOR  EEVIEAV. 

1.  Of  what  use  are  joints  in  the  human  skeleton  ? 

2.  What  are  the  three  conditions  of  a  good  movable  joint? 

3.  How  do  joints  of  the  body  compare  with  joints  of  a  machine? 

4.  Describe  the  use  of  articular  cartilage. 

5.  How  is  a  joint  lubricated  ? 

6.  What  provision  is  made  for  keeping  joints  in  place? 

7.  Give  examples  of  immovable  joints. 

8.  What  kind  of  joints  in  the  bones  of  the  face? 

9.  Name  three  important  kinds  of  movable  joints. 

10.  Describe  the  motion  of  the  atlas  on  the  axis. 

11.  What  kind  of  motion  in  a  hinge-joint? 

12.  Of  what  advantage  is  a  ball-and-socket  joint? 

13.  What  kind  of  joints  are  in  the  tarsus  and  carpus? 

14.  What  is  gout  f  what  is  one  of  its  causes? 

15.  What  are  some  of  the  causes  of  rheumatism  in  the  joints  ? 

16.  What  is  a  sprain  ? 

17.  What  is  a  dislocation  ? 

18.  Point  out  and  name  each  kind  of  movable  joint  seen  in  skele- 
ton on  page  34. 


CHAPTER   VI 

MOTION 

Motion  a  test  of  life. — Animals  have  the  power  of 
vohintary  inoveiiieiit.  Our  common  test  of  life  is  the 
ability  to  move.  Some  motion,  such  as  the  beating  of  the 
heart  or  the  act  of  breathing,  is  going  on  in  the  body  at 
all  times.  The  power  of  voluntary  movement,  however, 
is  one  of  the  chief  distinguishing  marks  between  the 
higher  animals  and  the  higher  plants. 

Movement  within  the  cells. — Beside  the  com- 
monly observed  motions  of  the  body,  there  are  also  many 
delicate  motions  which  are  never  seen  except  by  aid  of 
a  strong  microscope. 

The  motion  within  the  cell,  as  in  case  of  cell  division 
described  on  page  20,  is  an  evidence  of  the  life  of  the 
cell. 

The  white  corpuscle  is  capable  of  independent  move- 
ment, and  goes  about  from  j)lace  to  place  within  the 
body. 

Another  examjDle  of  cellular  movement  is  found  in  cer- 
tain of  the  epithelial  cells  which  are  provided  with  cilia 
(Fig.  19).  These  cilia,  some  thirty  to  each  cell,  are  in 
constant  motion,  lashing  back  and  forth.  This  motion  is 
produced  by  the  cell,  and  continues  long  after  the  body 
as  a  whole  has  ceased  to  live. 

59 


60  THIRD    BOOK    OF   PHYSIOLOGY 

Motion  by  means  of  muscles. — The  principal 
bodih-  motions  are  accomplished  by  the  action  of  the 
muscles  upon  the  bones.  One  important  use  of  the  skel- 
eton and  its  joints  is  to  give  the  body  agility  and  facility 
of  motion. 

The  skeleton  alone,  however,  has  no  power  of  motion. 
The  power  to  produce  motion  resides  chiefly  in  the 
muscles,  which  are  attached  to  the  bones.  They  are 
called  skeletal  muscles.  There  are  also  other  kinds  of 
muscle,  such  as  those  of  the  heart  and  arteries,  which 
will  be  described  later. 

The  two  ends  of  a  skeletal  muscle  are  attached  to  two 
different  bones,  which  have  a  movable  joint  between 
them.  When  the  muscle  contracts,  the  positions  of  the 
bones  are  changed  in  their  relation  to  each  other.     In 


Fig.  36. — Diagram  showing  how  motion  is  produced  by  contraction  of 

muscle. 


the  diagram  (Fig.  36)  the  muscle  is  attached  at  O  and  I. 
The  joint  is  at  J.  AVhen  the  muscle  shortens,  the  lines 
A  J  and  B  J  will  be  drawn  towards  each  other.  If  the 
point  O  is  immovable,  all  the  motion  will  be  made  by 
A  J.  Such  is  the  plan  of  most  skeletal  muscles.  It  is 
plain  that  if  the  two  ends  of  the  muscle  were  attached 


MOTIOX 


Gl 


to  the  Siime  bone    its  contractions  wonld  only  tend  to 
stniin  the  bone  and  tear  the  mnscle. 


Shape  and  attachment  of  muscles. — Skeletal 
muscles  consist  of  a  soft.  red.  central  part,  which  tapers 
off  at  each  end  into  cords  of  white  fibrous  tissue.  The 
coitls  are  called  tendons,  and  they  .serve  as  a  convenient 
means  for  the  attachment  of  muscles  to  bones.  Some 
muscles,  however,  are  attacheil  directly,  without  the  in- 
tervciition  of  tendons. 


Fig.  oT. — Showing  bones  of  the  arm  and  biceps  muscle. 

In  Fig.  37.  O  is  called  the  origin  of  the  muscle  and 
/the  insertion.  The  origin  is  the  end  nearest  the  centre 
of  the  body,  and  which  usually  moves  the  least.  In  the 
Fig.  is  a  representation  of  the  muscle  called  the  biceps. 
It  is  the  large  muscle  of  the  arm.  to  which  men  and  l>oys 
often  point  as  an  evidence  of  their  muscular  ability. 


62 


TITTPJ)    P,O0K    OF    PHYSIOLOGY 


It  has  its  origin  in  the  shoulder-blade  at  0,  and  its  in- 
sertion at  I.  When  it  contracts,  the  forearm  and  hand 
are  raised. 


Mechanical  principles  in  the  motions  of  the 
skeleton.— The  lever  is  the  chief  mechanical  con- 
trivance for  i^roducing  the  motions  of  the  body:  Levers 
are  usually  classed  as  three  kinds,  the  difference  depend- 
ing on  the  point  of  attachment  of  the  iceiffht.  the  powet', 


W 


© 


^ 


w 


© 


w 


@ 


■^ 


u 


Fig.  38.— Levers  of  the  first  class. 

and  the  fulcrum .  Tlie  fulcrum  is  alwaj'S  the  still  place, 
or  the  axis  upon  which  the  lever  rotates.  Fig.  38  shows 
three  levers  of  the  first  class.  The  bolts  show  the  posi- 
tions of  the  fulcrums.  The  hand  shows  the  point  where 
the  power  is  applied,  and  the  weight  or  resistance  to  the 
power  is  at  the  other  end. 


Mot  I  ox  03 

Tn  the  topmost  lrv<'r  Mh'  Iwo  aims  ai<'  ('(iiuil,  and  so 
there  is  no  a(hantaj;:(^  except  that  wlien  tlie  liand  i)uslie8 
down  the  weight  goes  up. 

In  the  second  lever  the  weight  end  is  niucli  lonj^'cr 
tlian  tlie  hand  end,  and  so,  wlien  tlie  hand  moves  down 
and  up,  the  weight  will  move  u])  and  down,  but  much 
farther  and  faster.  With  this  arrangement  the  hand  can 
move  only  a  light  weight,  but  it  can  move  it  rapidly. 

Tn  the  third  one  the  hand  has  the  long  arm  of  th«i 
lever.  The  weight  may  now  be  heavy,  but  it  can  be 
moved  up  and  dow^n  only  slowly. 

Not  much  use  is  made  in  the  body  of  this  first  class  of 
levers.  An  example  of  it  is  found  in  the  backward  move- 
ment of  the  head.  Here  the  fulcrum  is  the  point  where 
the  skull  articulates  with  the  atlas.  The  front  part  of 
the  head  is  heavier  than  the  part  back  of  this  fulcrum, 
and  so  the  head  will  fall  forward  of  itself  But  a  back- 
ward motion  is  produced  by  the  contraction  of  muscles 
which  are  attached  to  the  backbone  below  and  to  the 
occipital  bone  above. 

In  the  second  class  of  levers  the  fulcrum  is  at  one  end 
and  the  powder  at  the  other,  with  the  weight  between 
them.  In  this  arrangement  there  is  a  gain  in  power,  and 
the  closer  the  weight  is  to  the  fulcrum  the  heavier  it  may 
be  for  the  same  power  exerted  by  the  hand,  but  the  weight 
will  move  through  a  smaller  distance  and  less  rapidly 
than  the  hand  does.  A  good  example  of  this  kind  of 
lever  is  found  in  the  foot.  It  is  used  in  rising  on  the  toes. 
Here  the  toes  are  the  fulcrum,  the  power  is  applied  at  the 
heel,  and  the  weight  of  the  body  is  between. 


64 


THIED   BOOK   OF   PHYSIOLOGY 


When  the  strong  muscle  of  the  calf  contracts,  it  pulls 
upon  the  tendons  which  are  attached  to  the  heel  and  the 
body  is  raised. 


W 


© 


Fig.  39. — Levers  of  the  .«ecoiid  cla.ss. 

Every  step  we  take  in  walking  and  running  involves 
the  use  of  this  muscle  and  lever. 


W 


Fig.  40.— Lever  of  the  third  claas. 

Levers  of  the  third  class  are  most  common  in  the  body. 
Here  the  power  is  applied  between  the  fulcrum  and  the 
weight.     The  power,  in  this  kind  of  lever,  must  always 


MOTION  65 

bo  j^rciitcr  tliiiii  {\w  wci^lil,  or  rcsistiiiici',  but  tliero  is  ;i 
^SLin  in  (hr  vclointy  with  wliich  tiic  \v(^ii;lit  is  moved. 
The;  niovi'mcnt  by  wliicii  Die  liiiud  is  raised  to  Iheinouth 
is  accomplished  by  a  ]vv(iv  of  this  kind. 

By  reference  to  Fijj^.  M  it  is  seen  that  tlie  fulcrum  is  the 
elbow,  the  weij^ht  is  the  foi-earm,  the  hand,  and  what- 
ever the  hand  contains,  and  the  power  is  applied  to  the 
radius  a  little  way  below  the  elbow  at  the  point  of  inser- 
tion of  the  biceps. 

Voluntary  muscles. — Muscles  are  of  two  kinds, 
the  voluntary  and  the  involuntary.  The  voluntary^  as  the 
word  would  indicate,  are  those  which  are  under  the  con- 
trol of  the  mind  and  can  be  operated  at  will. 

When  you  nod  in  response  to  an  inquiry,  we  know  you 
mean  yes,  because  the  muscles  that  produce  that  motion 
are  voluntary'.  All  the  skeletal  muscles  are  volun- 
tary. 

Each  bundle  of  muscle,  as  we  shall  see  later,  is  made 
up  of  a  great  number  of  cells  with  the  cell  material  about 
them.  Each  cell  is  connected  by  a  nerve-thread  to  the 
nervous  centre,  — the  brain.  When  we  wish  any  voluntary 
muscle  to  do  work,  a  message  is  sent  out  along  the  nerve 
from  the  brain  to  the  muscle.  The  muscle  is  thus  stimu- 
lated to  activity.  Each  cell  of  the  muscle  contains  a 
store  of  energy  which  it  gets  from  the  food  we  eat.  When 
the  food  material  unites  with  the  oxygen  which  we 
breathe,  the  energy  is  changed  to  heat  and  work. 

The  energy  is  all  in  the  cell,  and  the  message  from  the 
brain  only  excites  the  cell  to  activity.     It  is  not  like  ring- 


66 


THIED   BOOK   OF   PHYSIOLOGY 


ing  an  electric  bell  by  pressing  a  button,  for  in  that  case 
all  the  energy  passes  over  the  wire  to  the  bell. 

The  relation  of  a  general  to  his  army  is  a  good  illustra- 
tion of  the  relation  of  the  brain  to  the  muscle.  The 
energy  is  in  the  army,  but  it  may  remain  perfectly  passive 
until  orders  are  received  from  the  general.     The  order 


Fig.  41. — Showing  the  shape  of  a  muscle  before  and  after  contraction. 

may  set  the  whole  army  in  motion.     Only  the  stimulus 
and  not  the  energy  came  from  the  general. 


Involuntary  muscles. — Involuntary  muscles  are 
those  over  which  the  mind  has  no  direct  control.  They 
are  such  muscles  as  are  found  in  the  walls  of  the  gullet, 
and  which  by  contractions  force  the  food  down  into  the 
stomach.  The  muscles  in  the  coats  of  the  stomach  are  of 
this  kind,  and  after  a  meal  they  contract  on  the  food, 
moving  it  about  and  mixing  it  with  the  digestive  juices. 
The  intestines  by  a  contraction  of  the  muscles  in  their 
walls  move  the  food  along  without  any  voluntary  atten- 
tion on  our  part.     The  action  of  the  heart  is  beyond  the 


MOMMON 


67 


control  of  the  will.  Its  muscles  are  therefore  involuntary. 
The  muscles  which  are  concerned  in  the  operation  of 
breathing  may  be  called  semi-voluntary,  for  they  can,  to 
some  extent,  be  controlled  by  the  will,  but  breathing  will 
continue  while  we  are  asleep,  or  while  we  are  completely 
absorbed  in  other  matters. 

It  must  not  be  thought  that  these  cells  move  purely  of 
their  own  accord.     They,  too,  are  stimulated  by  nerves 
which  come  from  nerve-centres, 
as  will  be  exj^lained  under  the 
discussion  of  the  nervous  system. 

Structure  of  voluntary 
muscle. — The  voluntary  mus- 
cles are  put  up  in  bundles  called 
fascicc.  The  fascice  are  bound 
with  connective  tissue,  and  are 
in  turn  made  up  of  smaller  bun- 
dles called  fasciculi,  five  of  which 
are  shown  in  Fig.  42.  The  fas- 
ciculi are  composed  of  fibres, 
which  are  the  cells  and  cell  mate- 
rial of  muscle. 

The  fibres  are  composed  of  a 
soft   substance   enclosed   in   a   sheath   called   the  sarco- 
lemma.     The  fibres  are  small,  having  an  average  diameter 
of  about  ^U  of  an  inch,  while  their  length  varies  from  i 
to  1\  inches. 

A  bundle  of  muscle  may  be  a  foot  or  more  long,  so  that 
a  fibre  cannot  always  reach  from  end  to  end  of  the  mus- 


FiG.  42.— Portion  of  fas- 
cia showing  live  fasciculi 
and  their  component  fibres. 


68 


THIRD    BOOK   OF   PHYSIOLOGY 


cle.  In  that  case  the  end  of  one  lies  between  two  others 
that  follow,  and  to  which  they  are  cemented  by  means 

of  the  sarcolemma. 

At  the  ends  of  skeletal  mus- 
cles the  fibres  blend  into  the 
tendons,  or,  if  there  be  no  ten- 
dons, they  connect  to  the  bone. 

When  the  fibre  is  examined 
by  a  strong  microscope,  it  is  seen 
to  be  marked  across  by  very  fine 
alternating  bands  of  dark  and 
light.  A  bundle  of  this  kind  of 
fibres  is  called  striped  or  striated 
muscle. 

Each  fibre  contains  a  nucleus, 
and  is  connected  by  a  nerve  to 
the  brain  so  that  it  can  be  made 
to  contract  at  will. 

Structure  of  involuntary 
muscle. — The  involuntary  mus- 
cles are  made  wp  of  spindle- 
shaped  fibres  Avhich  are  about 
43  0  of  an  inch  iu  length  and 
about  4oW  inch  in  breadth.  Each  contains  an  elongated 
nucleus. 

This  kind  of  muscle  is  used  to  surround  cavities  of  the 
bodj^,  cliiefly  the  digestive  tract  and  blood-vessels.  As 
they  are  not  attached  to  bones,  they  have  no  origin  or  in- 
sertion. 


Pig.  43. — Showing-  iiuis- 
cles  of  the  forearm  and 
their  tendons. 


MOTION 


C9 


The  fibros  are  not  striated  ;is  in  voluntary  muscles. 
They  slowly  contract  uiulcr  proper  stimulus,  becoming 
shorter,  and  thus  cliauging  the  capacity  <►("  tlu^  cavity 
which  thev  surround. 


Fir,.  44. — Striated  muscular  fibres. 

The  fibres  of  the  heart  partake  of  the  structure  of  both 
kinds  of  muscle.     Its  flattened  fibres  are  laced  together 


Ftg.  45. — Fibres  of  iuvuluntury  muscles. 

and  are  without  a  sarcolemma,  as  is  the  case  with  invol- 
untary muscles,  but  the  fibres  are  striped  as  in  voluntary 
muscles,  though  not  so  distinctly. 


The  development  of  muscle.— Muscle  is  capable 
of  high  development.     Our  bodies  are  made  in  such  a 


70  THIRD   BOOK   OF   PHYSIOLOGY 

way  that  when  any  organ  or  part  of  the  body  is  called 
upon  for  greater  and  greater  service  an  effort  is  made  to 
meet  the  demand. 

When  a  muscle  has  been  unused  for  a  long  time,  it 
degenerates,  until  but  little  is  left  of  it,  except  the  con- 
nective tissue. 

After  a  broken  arm  or  leg  has  been  in  the  splints  for 
several  weeks,  the  muscles  become  so  weak  that  it  requires 
long  and  careful  exercise  to  bring  them  back  to  their 
former  strength. 

The  brawny  arm  of  the  blacksmith,  on  the  other  hand, 
shows  the  effect  of  vigorous  daily  exercise.  Exercise  is 
a  call  for  power  which  nature  tries  to  furnish. 

Food  of  rauscle. — Each  muscular  fibre  or  cell,  as 
we  have  alread}^  explained,  is  a  little  engine  capable  of 
converting  food  into  heat  and  motion.  Just  like  other 
engines,  however,  they  cannot  give  out  any  energy  until 
they  first  receive  it.  Good  air  and  good  food  are  neces- 
sary to  the  development  of  strong  and  healthy  muscle. 
Without  these,  exercise  is  worse  than  useless. 

Development  gradual.— Many  young  people  try 
to  develop  the  muscle  too  rapidly.  They  sometimes 
choose  large  dumb-bells  for  their  gymnastic  exercises  and 
expect  to  see  great  results  in  a  few  days  or  weeks.  This 
is  a  mistaken  notion.  The  true  development  of  either 
body  or  mind  comes  gradually. 

Those  who  are  experienced  in  this  matter  give  more 
attention  to  the  regularity  and  persistence  in  their  practice 


MOTION  71 

than  to  tlie  intensity  ol'  it.  A  strong  man  can  profitably 
use  only  a  two-pound  (hinib-bell,  but  lie  must  piactisi*  a 
certain  len<;th  of  time  every  day  and  then  rest. 

When  exercise  is  carried  too  far,  the  muscle  becomes 
exhausted  and  weakened. 

Clothing  during  exercise.— In  a  later  chapter  we 
shall  see  that  one  office  of  the  skin  is  to  throw  otl"  wavSte 
matter  which,  if  retained  in  the  circulation,  would  be  a 
poison  to  the  blood.  During  vigorous  exercise  the  quan- 
tity of  waste  thrown  off  is  nuich  greater  than  at  other 
times,  and  for  this  reason  the  clothing  should  be  loose 
and  light.  The  same  kind  of  clothing  is  also  necessary 
for  the  freedom  of  the  nuiscles  and  to  i^ermit  the  escape 
of  the  excess  of  heat  which  is  always  developed  by  ex- 
ercise. 

Kinds  of  exercise. — There  are  a  great  many  kinds 
of  good  exercises.  The  kind,  however,  is  not  always  so 
important  as  the  way  it  is  done. 

As  a  rule,  it  may  be  said  that  outdoor  exercises  are 
good  for  bodily  development  because  of  the  wholesome 
air  and  sunshine. 

Also  those  exercises  which  call  into  use  many  muscles 
of  the  body  are  preferable. 

Walking  is  good,  inasmuch  as  it  takes  one  into  the 
open,  fresh  air  ;  but  if  the  Avalk  is  onl}-  a  stroll  about 
the  streets  it  fails  to  call  into  use  many  parts  of  the 
body.  The  best  kind  of  a  walk  is  one  up  and  down 
hills  and  over  fields  and  fences.  A  dress  parade  is  of 
little  value. 


72 


THIRD   BOOK   OF   PHYSIOLOGY 


Those  who  live  near  a  body  of  water  have  at  hand  a 
most  beneficial  kind  of  exercise  in  rowing,  which  should 

call  into  full  use  the  muscles  of 
tlie  arms,  legs,  and  back. 

Lawn  tennis  is  among  the 
best  of  outdoor  exercises. 

Base-ball  and  foot-ball  under 
a  proper  director  are  good  kinds 
of  sport,  not  only  for  the  exer- 
cise in  the  game  itself,  but  also 
because  success  comes  only  to 
those  who  take  good  care  of 
their  general  health  at  all  times. 

Physical  culture.— In  re- 
cent times  there  is  a  demand 
for  physical  culture  apart  from 
any  games.  This  can  be  se- 
cured, under  the  guidance  of  a 
competent  director,  in  the  gym- 
nasia of  the  best  schools  and 
colleges. 

In  any  game  there  are  some 
parts  of  the  body  which  receive 
an  undue  amount  of  exercise, 
and  other  parts  which  receive 
none,  or  not  enough  for  their  proper  development. 

In  physical  training  the  development  progresses  in  a 
systematic  and  natural  manner.  The  action  of  the  heart, 
lungs,  and  muscles  are  all  strengthened.     Those  who  are 


Fig.  46. — Exercisers 


MOTION  73 

MCiik  can  tluis  !)('  made  (it  locngaji^ti  in  streniioiis  athletic 
sport  without  haini  to  themselves.  Thii  general  health  is 
improved  by  sucii  culture,  and  the  chances  of  disejuse  and 
sickness  are  much  reduced. 

One  Diay  obtain  such  culture  at  home  by  use  of  dumb- 
bells, Indian  clubs,  and  exercisers  such  as  shown  in 
Fig.  4(>. 

iMore  important  than  the  apparatus,  however,  is  the 
will-power  needed  to  persist  in  taking  the  regular  daily 
exercise. 

It  is  best  always  to  first  consult  one  who  is  competent 
to  instruct  in  this  art,  that  the  many  errors  which  the  un- 
aided novice  is  sure  to  make  may  be  avoided. 

Whatever  the  nature  of  the  exercise  is,  the  conditions 
that  should  prevail  are  :  good  air,  many  muscles  in  use, 
moderation,  rest,  persistency  in  effort,  and  regularity  in 
time. 

Skilful  muscles. — The  development  of  a  strong  and 
healthy  body  is  desirable  for  several  reasons.  Such  a 
condition  has  associated  with  it  a  good  appetite  for  food 
and  ability  to  assimilate  it ;  a  vigorous  circulation  of 
blood ;  and  deep  breathing.  Such  a  condition  of  body 
furnishes  a  good  foundation  for  a  vigorous  and  sustained 
action  of  mind.  "A  sound  mind  in  a  sound  body"  is  a 
true  maxim.  It  is  not  necessary  for  this  purpose  that  the 
muscles  be  highly  developed,  ^but  that  they  should  receive 
sufficient  exercise  to  keep  them  in  a  healthy  and  vigorous 
condition. 

A  large  and  strong  muscle,  however,  is,  to  most  people. 


74  THIRD    BOOK    OF   PHYSIOLOGY 

of  no  advantage  in  itself.  Such  a  muscle  may  strike  a 
heavy  blow  or  lift  a  great  weight,  but  such  things  can  be 
done  by  the  brutes,  which  have  still  stronger  muscles. 
Man's  object  must  be  to  acquire  skill  in  the  use  of  his 
muscle. 

A  strong  muscle  that  is  trained  to  move  the  arms, 
hands,  legs,  and  body  in  a  skilful  manner  is  worth  all 
the  time  and  effort  which  such  training  requires. 

Effect  of  alcohol  on  the  muscles. — At  one  time 
it  was  thought  that  alcohol  would  add  strength  to  the 
muscles.  Its  true  nature  and  effect  upon  the  body  were 
not  then  known.  In  these  later  years  a  close  study 
of  the  subject  has  been  made  by  able  scientists  and 
physicians  who  were  interested  only  in  finding  out  the 
truth.  The  evidence  in  all  cases  is  that  the  use  of 
alcoholic  drinks  will  lessen  the  ability  of  the  muscles  for 
sustained  work,  and  the  man  who  relies  upon  the  use  of 
his  muscles  for  a  living,  cuts  down  the  soui'ce  of  his 
strength  by  the  use  of  alcohol. 

Of  course,  other  evil  effects  follow  the  use  of  alcohol, 
but  onlv  the  effect  on  muscle  is  beins^  considered  here. 

Experiments  with  the  ergograph. — The  ergo- 
graph  is  an  instrument  by  which  it  is  possible  to  tell 
quite  exactly  any  change  in  the  ability  of  muscles  to  do 
work.  Experiments  with  this  instrument  have  shown 
that  with  doses  as  small  as  one  and  one-half  teaspoonful 
of  alcohol  there  was  at  fi.rst,  for  a  short  time,  an  increase 
in  work.     But  soon  there  was  a  rai^id  drop  m  the  scale. 


MOTION  75 

so  that  llic  total  work  done  was  less  than  without  jilco- 
hol.  Many  experiments  of  this  kind  indicate  that  alco- 
hol has  a  depressinjr  effect  ujmmi  the  nmscles. 

Experiments  with  armies. — Tt  was  once  custom- 
ary to  deal  out  to  soldiers  rations  of  strong  drink,  such 
as  whiskey,  rum,  and  brandy.  This  was  done  because  it 
was  believed  that  the  soldier  could  then  endure  a  longer 
march  and  greater  fatigue  and  hardshii).  Trial  has  been 
made  with  soldiers  in  the  armies  of  the  United  States, 
England,  Germany,  and  other  nations,  with  the  use  of 
alcohol  and  without  it. 

The  results  clearly  showed  that  the  soldiers  without 
alcohol  were  in  much  better  physical  condition  at  the 
end  of  a  hard  contest  or  long  march.  Those  who  had 
taken  alcohol  would  start  out  more  briskly,  but  would 
sooner  fall  by  the  way. 

Alcohol  and  the  railroads.— All  good  railroads 
seek  to  do  business  on  an  economical  and  efficient 
basis.  To  do  this  they  must  have  efficient  men.  They 
have  found  that  alcohol,  even  in  moderate  quantities, 
will  sooner  or  later  lessen  a  man's  efficiency  for  service. 
The  officials  of  a  good  railroad  will  not  accept  the  ser- 
vices of  a  man  who  is  known  to  drink  any  kind  of  alco- 
holic liquors.  Some  will  not  even  permit  their  em- 
ployees to  lodge  or  board  at  a  hotel  which  has  a  bar 
attached.  Similar  precautions  are  taken  by  all  large 
business  firms. 

This  is  not  so  much  because  these  corporations  are 


7G  THTHD   BOOK   OF   PHYSIOLOGY 

interested  in  the  temperance  problem,  but  they  want 
those  men  who  can  l3est  do  their  work.  They  know  from 
experience  that  a  good  man  will  l>e  better  if  he  is  a  total 
abstainer  from  alcoholic  liquors. 

Athletics  and  alcohol. — Those  who  train  for  ath- 
letic contests,  where  they  will  need  all  the  strength  and 
power  of  endurance  they  can  muster,  are  required  to 
totally  abstain  from  the  use  of  tobacco  and  alcohol.  Ex- 
perience has  shown  the  trainers  that  these  two  poisons 
are  destructive,  and  tend  to  tear  down  and  not  to 
build  up. 

Even  those  who  follow  the  ignoble  calling  of  prize 
fighting  are  compelled  to  be  total  abstainers,  at  least 
during  their  period  of  training. 

A  young  man  who  belongs  to  the  boat-crew  or  foot- 
ball team  of  one  of  the  great  colleges  could  not  more 
efFectivel}'  disgrace  himself  in  the  eyes  of  his  fellow- 
students  than  by  using  alcohol  or  tobacco  on  the  eve 
of  an  important  contest. 

Effect  of  alcohol  on  skill. — Most  people  are  not 
directly  concerned  in  athletic  sports,  but  the  same  prin- 
ciple that  makes  it  advisable  to  refrain  from  alcohol  in 
that  case  will  more  forcibly  apply  in  the  serious  contests 
of  life.  The  degree  of  skill  needed  to  make  one  a  suc- 
cess in  any  art  is  acquired  only  by  long  practice  under 
favorable  physical  conditions.  Alcohol  so  affects  the 
nerves  and  muscles  that  the  nerve  is  not  able  to  deliver 
a  clear-cut  order  to  the  muscular  cell,  or  the  cell  is  not 


MOTION  77 

a])l('  to  execute    the  order.      The  result  is  an  uiistrady 
aud  clunisy  motion. 

It  is  claiiiM'd  on  <^ood  authority  that  the  present  com- 
mercial supnunacy  of  the  United  States  is  in  good  part 
due  to  the  fact  that  there  is  less  drinking  among  our 
workmen  than  among  those  of  European  countries. 
The  result  must  be  the  acquisition  and  retention  of  an 
artistic  skill  which  results  in  a  better  and  larger  output 
of  goods.  The  Labor  Bureau  of  the  United  States  shows 
iu  its  report  that  a  large  per  cent,  of  the  employers  of 
skilled  and  unskilled  labor  require  total  abstinence  on 
the  part  of  their  employees.  They  are  not  even  willing 
that  their  men  should  drink  after  their  day's  work  is 
done,  for  both  experience  and  exact  experimentation 
have  shown  that  alcoholic  drinks  taken  at  night  impair 
working  ability  the  following  day. 

QUESTIONS   FOR   REVIEW. 

1.  What  is  our  common  test  of  life? 

2.  Describe  some  movements  in  the  body  which  we  do  not 
ordinarily  observe. 

3.  How  are  nuiscles  attached  in  reference  to  joints?    Why? 

4.  What  is  meant  by  origin  and  insertion  of  muscle  ?  Illustrate 
by  reference  to  the  biceps. 

5.  Show  the  advantages  and  disadvantages  of  levers  of  the  first 
class.     Where  in  the  body  is  this  lever  used? 

6.  What  is  the  position  of  fulcrum,  power,  and  xceight  in  levers 
of  the  second  class?      Give  example  of  its  use  in  the  body. 

7.  When  is  a  lever  of  the  third  class  ?  Give  example  of  its  use 
in  the  body. 

8.  Which  kind  of  lever  is  most  used  in  the  body?  What  is  tlie 
effect  on  bodilv  motions  ? 


78  THIED   BOOK   OF   PHYSIOLOGY 

9.  What  are  voluntary  muscles  ?    AVhere  are  they  located  ? 

10.  How  are  muscles  stimulated  to  activity? 

11.  Is  the  energy  in  the  nerves  or  in  the  muscles?     Illustrate  by 
the  relation  of  a  general  to  his  army. 

12.  AVhere  are  the  involuntary  muscles ?    Why  so  called? 

13.  Explain  the  structure  of  voluntary  muscles. 

14.  Explain  the  structure  of  involuntary  muscles. 

15.  What  is  peculiar  about  the  structure  of  heart  muscle? 

16.  How  can  muscle  be  developed  ? 

17.  Why  do  working  muscles  need  food? 

18.  Why  cannot  muscle  be  developed  rapidly? 

19.  What  kind  of  clothing  is  best  during  exercise?    Why? 

20.  Name  some  good  exercises.     Give  reasons. 

21.  How  does  physical  culture  differ  from  exercise  in  games  ? 

22.  AVhy  is  skill  desirable  ? 

23.  What  is  the  effect  of  alcohol  on  muscle  ? 

24.  What  is  shown  by  the  ergograph  ? 

25.  What  has  been  the  experience  with  armies? 

26.  What  is  the  action  of  railroad  officials  in  regard  to  alcohol? 
Why? 

27.  Wh}'  do  those  who   train  for   athletic  contests   not  drink 
alcohol  ? 

28.  What  is  the  effect  of  alcohol  on  skill? 


CHAPTER   VII 

FOODS 

The  use  of  food. — Our  l)Oflies  need  food  for  two 
purposes,  first,  to  build  up  and  maintain  the  tissues  of 
the  body,  and,  second,  to  furnish  the  energj^  needed  for 
the  ivork  we  have  to  perform  and  the  heat  which  must  be 
maintained  in  the  body. 

Nature  has  given  to  all  animals  the  sensations  of 
hnnger  and  thirst,  and  an  appetite  for  those  things 
which  the  tissues  need.  A  perfectly  healthy  appetite 
should  be  a' safe  guide  in  choosing  food.  Most  appetites, 
however,  are  not  reliable,  and  for  this  reason,  among 
others,  food  is  a  proper  subject  for  intelligent  study  both 
as  to  its  nature  and  its  use  in  the  body. 

Constant  loss  of  material  from  the  body. — 
There  is  constantly  being  thrown  off  from  the  body  in 
various  ways  a  quantity  of  matter  which  would  be  in- 
jurious if  retained  in  the  body,  or  which  is  no  longer  of 
any  use.  Every  breath  from  the  lungs  carries  out  con- 
siderable water  and  carbon  dioxide  :  by  perspiration  the 
skin  is  constantly  giving  off  water  and  waste ;  a  large 
amount  of  water  and  urea  is  excreted  by  the  kidneys ; 
the  undigestible  parts  of  food  as  well  as  the  undigestible 
matter  which  is  eaten  with  food  are  daily  thrown  off' 
from  the  body  ;  and  the  surface  epithelium  is  constantly 

79 


80  THIRD   BOOK   OF   PHYSIOLOGY 

wearing  away  and  falling  off.  From  all  such  causes  the 
body  loses  on  an  average  about  nine  ijounds  each  day. 

It  is  plain  that  at  this  rate  the  l)ody  would  soon  waste 
away  unless  food  be  supplied  at  the  same  rate. 

The  nine  pounds  a  day  is  for  the  average  healthy  body 
at  work  at  its  full  capacity.  When  food  is  not  sufiQcient 
to  supply  the  loss,  the  waste  will  be  less,  but  the  body 
will  be  less  efficient  in  the  same  proportion. 

Loss  of  energy. — The  old  idea  of  food  was  that  it 
was  only  for  the  purpose  of  supplying  the  tissues  with 
material  for  their  growth  and  repair,  and  to  lubricate 
the  moving  parts.  The  real  nature  of  food  was  not  un- 
derstood. We  now  know  that  the  chief  function  of  food 
is  to  supxjly  energy.  Every  motion  and  action  of  the 
body,  even  thinking  itself,  is  a  use  of  energy  which  was 
in  the  food.  When  the  body  does  any  work  it  must 
lose  a  certain  amount  of  energy,  and  is  to  that  extent  less 
able  to  do  other  work. 

When  the  body  does  very  little  work,  not  so  much 
food  need  be  eaten,  for  the  energy  from  the  food  last 
taken  has  not  yet  been  expended.  When  much  work  -is 
done  the  energy  is  soon  exhausted,  and  we  are  made 
aware  of  the  fact  by  the  sensation  of  hunger. 

Two  kinds  of  energy. — There  are  two  kinds  of 
energy,  called  the  potential  and  the  l-lnetic.  The  water 
in  a  dam  has  potential  energy  because  it  would  flow 
down  the  valley  if  the  dam  were  removed.  A  weight 
on  a  shelf  has  potential  energy  because  it  will  fall  if  the 


FOODS  81 

shelf  is  removed.  Coal  has  a  p<>teiitial  enerj]:y  bc^caiise  it 
h;us  a  strong  allinity  for  uxyg<Mi  and  w  ill  unite  with  it, 
producing  the  intense  heat  of  combustion.  Material 
bodies  in  general  possess  potential  energy  by  virtue  of 
their  position  ur  chemical  character.  Food  contains 
potential  energy  because  in  the  body  it  combines  with 
oxygen  and  is  changed  to  other  substances. 

The  result  of  all  such  changes  is  the  energy  of  motion 
which  is  called  kinetic  energy. 

The  main  purpose  of  food  is  that  we  may  take  into 
our  bodies  potential  energy,  which  may  there  be  con- 
verted into  kinetic  or  moving  energy  by  means  of  which 
we  move,  work,  think,  and  keep  warm. 

There  is  a  large  amount  of  energy  in  the  world,  and  the 
amount  never  grows  any  larger  or  smaller  as  a  result  of 
any  changes  which  we  can  bring  about. 

Our  chief  concern  must  be  to  keep  the  body  in  such 
a  state  of  health  that  the  necessary  amount  of  energy 
may  be  appropriated  by  it  and  made  to  do  useful  work. 

Comparison  with  steam-engine. — The  relation 
of  coal  to  the  steam-engine  may  serve  in  part  as  an  illus- 
tration of  how  food  is  converted  into  ability  to  do  work. 
The  fuel — coal,  wood,  or  gas — is  made  to  unite  with 
oxygen  under  the  boiler.  An  intense  heat  is  generated, 
which  is  carried  by  the  steam  to  the  engines,  and  there 
converted  into  the  motions  of  the  machines  of  the  mills 
and  factories. 

After  the  fire  is  once  started,  the  boilers  and  engine, 

if  kept  in  repair,  will  continue  to  do  the  work  to  which 

6 


82  THIED   BOOK   OF   PHYSIOLOGY 

they  are  adapted  as  long  as  they  receive  their  proper  food, 
which  is  coal  or  some  form  of  carbon. 

AVhen  the  fireman  cuts  off  the  supply  of  fuel,  the  en- 
gine runs  slower  and  slower,  and  finally  becomes  still  and 
cold. 

While  the  engine  is  running,  its  whole  operation  con- 
sists in  getting  energy  from  the  fuel  and  passing  it  on  in 
some  form  to  other  objects  upon  which  it  does  work. 

The  coal  is  the  source  of  the  energy  of  the  engine  in 
about  the  same  way  that  food  is  the  source  of  the  energy 
of  the  human  body.  The  method  by  which  the  change  is 
brought  about,  however,  is  different  in  many  particulars. 

Oxidation  in  the  human  body.— The  one  im 
portant  particular  in  which  the  coal  of  the  engine  and 
the  food  of  the  body  are  exactly  alike  is  the  strong  af&nity 
of  both  for  oxygen.  Their  potential  energy  consists  in 
the  fact  that  they  can  be  oxidized,  that  is,  thej"  will  com- 
bine with  oxygen,  or  burn.  By  this  process  the  energy 
is  made  available. 

In  the  case  of  the  engine  the  fuel  is  all  oxidized  rapidly 
and  with  intense  heat  at  one  place,  that  is,  in  the  fire-box. 
In  the  body  oxidation  takes  place  slowly  and  in  all  parts 
of  the  body.  Food  is  carried  in  the  stream  of  blood  to 
all  the  cells  and  there,  for  the  most  part,  it  is  burned,  and 
its  potential  energy  becomes  kinetic  or  moving  energy. 
The  most  of  the  oxidation  occurs  in  those  cells  which  are 
most  concerned  in  the  performance  of  work,  as  in  the 
muscles. 

Oxidation  within  the  body  does  not  result  in  a  high 


FOODS  83 

temperature  like  that  from  hmiiiiig  wood  or  (M»al.  In 
fact,  it  is  quite  certain  thai  much  of  the  energy  of  food  is 
converted  into  the  energy  of  motion  without  any  heating. 
Some  of  it  is  converted  into  lieat  energy,  and  thus  the 
temperature  at  which  the  body  can  best  live  is  main- 
tained. 

The  difference  in  the  rapidity  of  oxidation,  such  as 
occurs  in  a  stove,  and  that  within  the  body,  may  be  ill  us- 
trated  by  use  of  a  magnesium  ribbon.  When  a  piece  is 
lighted  in  the  open  air  it  will  rapidly  oxidize,  that  is, 
burn.  A  piece  of  the  same  material  placed  in  a  bottle 
and  moistened  with  a  few  drops  of  water  will  also  com- 
pletely oxidize,  but  will  require  several  days  to  do  so. 
The  total  amount  of  heat  produced  is  the  same  in  both 
cases  if  the  same  amount  of  material  is  used. 

Composition  of  the  body. — The  tissues  of  the 
body  are  found  to  be  composed  mainly  of  four  elements, 
— carbon,  hydrogen,  oxygen,  and  nitrogen.  In  addition  to 
these  a  number  of  other  elements  are  also  found,  thousrh 
in  less  quantity.  They  are  sulphur,  phosphorus,  chlorine, 
sodium,  potassium,  calcium,  magnesium,  and  iron. 

The  three  main  compounds  in  the  body.— 

The  elements  named  above  do  not  exist  separately  in  the 
tissues,  but  are  united  in  a  variety  of  ways  forming  com- 
pounds. The  most  important  compound  is  proieid.  It 
is  found  only  in  live  matter  of  animals  and  plants,  and 
is  composed  of  carbon,  oxygen,  nitrogen,  hydrogen,  and 
sulphur.     A  good  examj)le  of  a  proteid  is  the  white  of 


84  THIRD    BOOK   OF   PHYSIOLOGY 

an  egg.     It  is  imi)ortaut  to  notice  that  proteid  contains 
nitrogen. 

The  second  class  of  imi^ortant  compounds  in  the  body 
are  the  carbohydrates.  These  are  composed  of  carbo7i, 
hydrogen^  and  oxygen,  but  no  nitrogen.  One  important 
carbohydrate  is  glycogen,  which  is  found  in  large  quanti- 
ties in  the  liver.  Others  are  grape  sugar,  muscle  sugar, 
and  milk  sugar.  These  are  all  closely  related  to  starch, 
from  which  they  can  be  made. 

The  third  important  comx:>ound  is  fat.  This  substance, 
like  the  carbohydrates,  is  composed  only  of  carbon, 
hydrogen,  and  oxygen,  but  in  different  proportion.  The 
quantity  of  fat  in  the  body  varies  greatly  in  different  in- 
dividuals and  in  the  same  individual  at  different  times, 
but  the  average  quantity  in  a  man  is  about  six  pounds. 

Other  substances  in  the  body. — The  three  classes 
of  substances  just  named  are  the  important  organic  com- 
pounds of  the  body.  There  are  also  several  other  sub- 
stances which  are  not  important  in  themselves,  but  which 
are  indispensable  because  of  the  assistance  they  give  in 
the  processes  of  life. 

Water  constitutes  about  two-thirds  of  the  weight  of 
the  body.  If  a  man  weighs  one  hundred  and  fifty  pounds, 
one  hundred  i^ounds  are  water.  Every  tissue  of  the  body 
contains  some  water.  Even  the  enamel  of  the  teeth,  the 
hardest  substance  in  the  body,  is  2  per  cent,  water. 
Muscle  is  three- fourths  water.  Bone  is  about  22  per 
cent,  water,  and  saliva  is  almost  -pure  water. 

Salt  is  found  in  all  tissues  of  the  body. 


FOODS  8.1 

Phosphate  and  carbonate  of  lime  are  tlie  chief  constitu- 
ents of  the  bones  and  the  teeth. 

A  number  of  either  compounds  are  also  found  in  the 
body. 

What  is  a  food. — Foods  should  l>e  such  sul:)stances 
as  will  sup])ly  the  material  of  which  we  find  the  body  is 
composed.  A  sutetance  is  not  a  foo<l  simply  Ijecause  it 
contains  elements  which*  are  found  in  the  bo<ly.  but  it 
must  be  of  such  a  character  that  it  can  be  digested  and 
made  a  part  of  the  body.  A  food  is  anything  ichich,  when 
taken  into  the  blood,  will  supply  the  needs  of  the  body  without 
doing  it  harm. 

Food  of  the  body  a  complex  compound. — Car- 
bon is  an  important  element  in  food,  but  carbon  alone  is 
not  a  food.  Charcoal  is  almost  pure  carbon,  but  it  can- 
not be  digested  or  in  any  way  l^ecome  a  part  of  the  body. 
Neither  can  the  body  make  any  use  of  hydrogen  or  nitro- 
gen as  foods.  Oxygen  is  the  only  element  which,  when 
uncombineil  with  other  elements,  may  be  considered 
a  food. 

The  chemist  writes  CeHioOe  as  the  symbol  for  grape 
sugar.  When  the  carbon,  hydrogen,  and  oxygen  are 
united  in  this  kind  of  a  complex  compound,  the  body 
can  use  them  as  food.  In  the  body  the  sugar  unites  with 
the  oxygen  which  we  breathe,  and  the  result  is  a  breaking 
down  of  the  sugar  compound  into  the  simpler  substances, 
water  and  carbon  dioxide.  In  this  way  the  energy  which 
was  in  the  sugar  is  set  free  for  work  or  heat 


86  THIRD    BOOK    OF   PPIYSIOLOGY 

The  compounds  of  fats  and  proteids  are  still  more 
complex  than  that  of  sugar,  but  they,  too,  unite  with 
oxygen,  and  are  broken  up  into  simpler  compounds  with 
the  like  result  of  a  liberation  of  energy. 

Three  classes  of  foods. — Froteid  is  an  essential 
food.  It  alone  contains  the  nitrogen  of  food,  and  is  the 
chief  source  of  supply  of  that  element  to  the  body. 
Proteid  is  built  up  by  vegetables.  From  this  source 
animals  obtain  it.  Lean  meat  is  rich  in  proteid.  Since 
man's  food  consists  of  both  meat  and  vegetables,  he  gets 
proteid  from  both  sources. 

The  chief  sources  of  i^roteid  are  meat,  milk,  eggs,  and 
vegetables,  — principall}^  wheat. 

The  carbohydrates  of  food  are  chiefly  obtained  direct 
from  the  starch  and  sugar  which  are  stored  up  in  vege- 
tables. The  chief  sources  are  wheat,  rice,  and  other 
cereals,  potatoes,  fruit,  cane  sugar  and  grape  sugar. 

The/«/s  of  food  are  obtained  from  a  variety  of  sources, 
such  as  fat  meats,  butter,  cream,  and  oils. 

Wheat  as  a  food. — Bread  is  often  called  ''the  staff 
of  life.'*  An  examination  of  a  grain  of  wheat  shows 
that  it  is  rich  in  the  foods  just  described.  It  contains 
about  14  per  cent,  of  i^roteids,  57  per  cent,  of  starch,  5 
per  cent,  of  grape  sugar,  2  per  cent,  of  fats,  and  many 
other  substances  in  small  quantity. 

The  proteid  of  wheat  is  mainly  the  gluten.  It  is  this 
which  makes  the  dough  sticky  and  tenacious. 

When  yeast  is  added  to  the  mass  of  dough  it  begins  to 


FOODS  87 

ferment  iind  ronii  alcohol  and  carbon  dioxide.  In  this 
way  bubbles  of  yas  ar(^  formed  in  every  part  of  the 
douj^h  and  are  held  in  by  the  tenacious  gluten.  The 
formation  of  the  gas  causes  the  bread  to  '^  rise."  In  the 
hot  oven  the  bread  rises  rapidly  because  the  heat  causes 
a  rapid  expansion  of  the  ga«.  When  it  is  baked  the  gas 
can  escape,  but  the  bread  retains  the  light  and  porous 
character  given  to  it  by  the  bubbles  of  gas. 

Wheat  contains  more  gluten  than  any  other  cereal,  and 
consequently  its  flour  can  be  most  easily  made  into  light 
bread. 

Corn. — Corn  contains  only  a  little  more  than  half  as 
much  of  the  proteids  as  compared  with  wheat,  but  a 
greater  per  cent,  of  starch,  and  it  is  the  richest  of  all 
cereals  in  fats.  Corn  holds  a  place  along  with  wheat  as 
one  of  the  valuable  vegetable  foods. 

Some  other  vegetables. — Peas  and  beans  are  about 
half  starch,  but  they  are  rich  in  proteids,  containing  about 
25  per  cent. 

Eice  is  about  four-fifths  starch,  but  is  poor  in  proteids. 
Rice  alone  is  a  poor  diet. 

Potatoes  are  poor  in  both  proteids  and  starch. 

Many  fresh  vegetables  are  valuable  articles  of  diet, 
though  they  are  mainly  composed  of  water  and  salts. 
That  the  body  needs  them  is  shown  by  the  fact  that  a  dis- 
ease called  scurvy  will  break  out  among  those  who  are 
compelled  to  eat  only  meats.  Such  has  often  been  the 
case  with  sailors  on  a  long  voyage,  or  men  in  other  situa- 
tions where  they  cannot  get  fresh  vegetables. 


88  THIED    BOOK    OF   PHYSIOLOGY 

Animal  food.— A  very  common  food  is  the  flesh  of 
animals.  This  consists  of  muscles,  fat,  and  the  various 
other  tissues  mingled  with  them.  Flesh  is  rich  in  proteid 
of  various  kinds,  the  chief  one  being  myosin.  Gelatin  is 
derived  from  the  white  fibrous  tissue.  Several  mineral 
foods  are  also  obtained  from  meats. 

Good  meat  that  is  well  cooked  is  a  valuable  food  for 
adults,  particularly^  for  those  engaged  in  heavy  work  or 
severe  exercise. 

Eggs  are  rich  in  proteid,  both  the  "white"  and  the 
"yellow."  All  the  food  material  necessary  for  starting 
the  chick  are  in  the  egg. 

Milk  is  nature's  food-mixture,  and  is  a  comj)lete  food 
for  infants.  For  adults  it  is  not  a  complete  food,  as  it 
does  not  contain  the  various  kinds  of  food  in  the  proper 
proportion.  From  milk  we  get  cream  and  butter,  which 
are  the  fats ;  milk  sugar,  which  is  a  carbohydrate  5  and 
casein,  or  cheese,  which  is  the  proteid. 

The  need  of  a  mixed  food. — Some  foods  contain 
all  the  different  kinds  needed  by  the  body,  but  not  in  the 
right  proportion.  Xo  one  food  makes  a  complete  diet, 
except  milk  for  infants.  It  is  estimated  that  a  man  doing 
a  moderate  amount  of  work  will  use  up  about  4000  grains 
of  carbon  and  300  grains  of  nitrogen  each  day.  He  will 
then  need  food  which  contains  this  amount  of  these  ele- 
ments. If  he  takes  more  carbon  or  nitrogen  than  the 
body  needs,  the  excess  will  not  only  do  the  body  no  good, 
but  will  add  to  the  labor  of  the  various  organs  to  get  rid 
of  it. 


FOODS  89 

For  exanii^lc,  meat  alone  in  sufTioiont  quantity  to  yield 
the  necessary  amount  of  carbon  would  also  yield  three 
times  the  amount  of  nitroj^cn  needed.  When  uieat  is 
eaten  with  bread  and  other  ve*^etables  the  proper  propor- 
tion of  the  food  elements  may  l>e  supplied  without  the 
excess  of  any  one. 

Amount  of  food. — ^lost  food  is  eaten  for  the  en- 
ergy it  contains,  and  the' work  which  it  enables  a  man  to 
do.  It  is  evident,  then,  that  a  man  needs  more  food  when 
he  is  hard  at  work  than  when  he  is  at  rest  or  engaged 
only  in  mild  forms  of  exercise. 

As  to  how  much  food  the  body  needs,  it  is  not  yet  pos- 
sible to  give  a  definite  answer.  The  authointies  do  not 
agree  on  this  matter.  It  is  quite  certain,  however,  that 
most  people  err  in  eating  too  much  rather  than  too  little. 
According  to  a  standard  which  has  been  largely  followed, 
it  is  assumed  that  a  man  doing  moderate  work  would 
need  118  grams  of  proteid,  56  grams  of  fat,  and  500  grams 
of  carbohydrates  per  day. 

The  total  fuel  value  of  this  amount  of  food  is  3055  large 
calories.'-' 

Recent  exxjeriments  would  indicate  that  an  amount  of 
food  whose  fuel  value  is  only  1600  large  calories  is,  when 
properly  digested  and  assimilated,  better  both  for  health 
and  ability  to  do  strenuous  work. 

If  excess  of  food  were  only  so  much  matter  to  be  re- 

*  A  large  calorie  is  the  amount  of  lieat  needed  to  raise  the  tem- 
perature of  one  kilogram  of  water  one  degree  centigrade. 


90  THIED   BOOK   OF   PHYSIOLOGY 

fused  and  cast  off  by  tlie  body,  it  would  not  be  a  matter 
of  particular  concern.  But  the  organs  of  digestion  and 
excretion  make  an  effort  to  handle  all  of  it.  They  are 
overtaxed,  and  none  of  their  work  is  done  well.  Such 
ill-13repared  food  may  even  be  a  poison  to  the  tissues  and 
work  great  evil  to  the  health  of  the  body. 

The  cooking  of  foods. — Cooking  is  practised  bv  all 
civilized  peox^le.  and  is  indispensable  in  the  preparation 
of  certain  kinds  of  food.  The  carbohydrates,  which  are 
mainlv  starch,  form  tlie  laro'er  bulk  of  foods.     AVhen  the 


Fig.  47. — Triehinfe  in  pork. 

Starch  is  cooked,  it  is  much  more  readily  soluble  in  the 
juices  employed  in  its  digestion. 

Meats  are  not  only  more  palatable  when  properly  jjre- 
pai'cd  in  the  kitchen,  but  the  tissues  are  softened,  and 
can  be  more  finely  divided  by  mastication,  and  more 
readily  dissolved  by  the  gastric  juice  in  the  stomach. 

Another  good  reason  for  cooking  some  foods  is  that  any 
minute  living  organisms  which  might  be  present  may  be 
destroyed  by  the  intense  heat.  This  is  particularly  true 
of  i^ork.  lu  Fig.  47  is  a  specimen  of  diseased  pork,  as  it 
appears  under  the  microscope,  showing  trichinae  coiled 
up  in  the  tissue.  These,  if  eaten,  may  lodge  in  the  tissues 
of  the  body.     Thorough  cooking  will  kill  them. 


FOODS  01 

Rules  and  methods  of  cooking  cannot  be  given  in  a 
book  of  this  character.  Many  books  are  written  and 
schools  established  for  instruction  in  this  useful  art.  A 
general  knowledge  of  the  best  ways  to  prepare  food  would 
be  of  the  jrreatest  vahie  to  tho  human  nice. 

Is  alcohol  a  food  ? — Any  substance  which  at  first 
seems  to  supply  the  body's  needs,  but  which  in  time 
works  a  serious  injuiy,  is  not  a  food. 

The  sj'mbol  which  the  chemist  uses  for  alcohol  is 
CJIgO.  Since  carbon,  hydrogen,  and  oxygen  are  essen- 
tial parts  of  the  tissues  of  the  body  and  of  our  foods,  it 
might  at  first  appear  that  alcohol  would  be  a  desirable 
food. 

^Mleu  we  consider  a  number  of  other  compounds,  how- 
ev^er,  which  also  contain  elements  found  in  the  body,  but 
which  we  know  to  be  poisonous,  we  see  that  our  inference 
in  regard  to  alcohol  is  not  correct.  Hydrocyanic  acid, 
for  example,  is  a  deadly  poison.  A  very  small  quantity 
of  it  will  kill  almost  instantly,  and  yet  it  is  made  up  of 
hydrogen,  carlxm.  and  nitrogen,  its  symbol  being  HCX. 

Again,  we  know  that  alcohol  will  oxidize. — that  is.  it 
will  burn  and  yield  heat  and  energy. 

Alcohol  will  also  oxidize  in  the  human  body  and  yield 
a  certain  amount  of  heat  and  energy.  Since  this  is  one 
of  the  most  important  functions  of  food,  it  would  appear 
that  alcohol  would  be  a  food. 

A  true  food,  however,  will  yield  heat  and  energy  with- 
out doing  any  harm  to  the  organs  and  tissues  of  the  bodj*. 
Alcohol,  while  it  yields  heat  and  energy,  acts  at  the  same 


92  THIED    BOOK    OF    PHYSIOLOGY 

time  as  a  poison.     For  this  reason  alcohol  cannot  be 
classified  as  a  food. 

This  may  be  illustrated  in  this  way  :  It  is  vrell  known 
that  when  sulphuric  acid  and  water  are  mixed  together 
in  about  equal  parts,  the  mixture  will  become  very  hot. 
This  acid  will  also  corrode  and  "eat  up"  iron.  Suppose 
now  that  an  engineer  sliould  adopt  the  plan  of  mixing 
sulphuric  acid  witli  the  water  in  the  boiler  when  he 
wanted  to  "get  ui>"  steam.  The  water  would  be  rapidly 
heated,  and,  to  an  ignorant  person,  this  would  seem  to 
be  a  good  plan.  It  would  soon  be  found,  however,  that 
the  material  of  the  engine  was  being  rapidh^  destroyed 
by  the  acid,  and  either  this  method  of  getting  energy 
would  have  to  be  discontinued  or  the  boiler  would  soon 
need  to  go  to  the  shop  for  repairs  or  be  abandoned  alto- 
gether. 

QUESTIONS   FOR   REVIP:W. 

1.  State  the  two  chief  purposes  of  food. 

2.  "What  are  some  of  the  ways  by  which  the  body  loses  in  weight? 

3.  AVhat  was  an  old  idea  about  the  purpose  of  food  ? 

4.  AVhy  does  a  man  get  hungr}-  sooner  when  he  works  tlian 
when  he  is  idle  ? 

5.  What  are  the  two  kinds  of  energy? 

6.  Explain  what  is  meant  by  potential  energy. 

7.  How  does  a  steam-engine  get  its  energy  ? 

8.  AVhat  difference  in  the  use  of  food  in  a  steam-engine  and  in 
man  ? 

9.  How  does  the  body  get  energy  from  food? 

10.  Where  did  the  food  get  its  energy  ? 

11.  What  difference  in  the  kind  of  oxidation  in  an  engine  and 
in  a  human  body? 


F()OJ)S  ^''* 

12.  Name  the  four  elements  of  which  the  body  is  largely  com- 
p<^tHl.     Name  i?everal  others. 

l.S.  What  are  the  three  chief  comiMumd.s  of  the  binly  ?  What  is 
their  composition? 

14.  How  much  of  the  body  is  water? 

15.  Define  a  foinl. 

10.  Why  must  the  food  of  the  body  be  complex  compounds? 

17.  What  element  of  food  is  found  only  in  ])roteid? 

18.  How  are  proteids  formed? 

19.  What  kinds  of  foods  ftirnish  us  with  proteids? 

20.  What  kind  of  foods  furnish  carbohydrates? 

21.  What  is  the  source  of  fats? 

22.  What  makes  wheat  a  good  food? 

23.  Explain  the  rising  of  bread. 

24.  How  does  corn  differ  from  wheat  as  a  foo<l  ? 

25.  What  shows  that  the  body  needs  fresh  vegetable  food? 
2G.  Name  and  tell  the  value  of  several  animal  foocLs. 

27.  Why  is  a  mixed  diet  necessary? 

28.  How  much  should  one  eat? 

29.  What  evil  results  follow  from  excessive  eating? 

30.  What  is  the  use  of  cooking? 

31.  How  can  proper  methods  of  cooking  be  learned? 

32.  What  are  trichime? 

33.  Is  alcohol  a  food?  What  makes  it  seem  to  be  a  food?  Why 
is  it  not  a  food  ? 

34.  What  will  a  good  food  do  for  a  body? 

35.  How  does  alcohol  differ  from  a  food  ? 

36.  Illustrate  by  the  action  of  sulphuric  acid  on  the  boiler  of  an 
engine. 

EXPERIMENTS. 

Test  for  proteid.— The  white  of  an  egg  is  nearly  pure  proteid.  Stir  the 
white  of  an  egg  into  about  one-half  pint  of  water,  and  tilter.  Put  some  of  the 
solution  into  a  test-tube  or  bottle  and  add  to  it  some  nitric  acid.  Note  the  change 
to  a  yellow  color.    Add  ammonia  and  the  color  will  change  to  an  orange. 


94  THIED   BOOK    OF   PHYSIOLOGY 

This  test  for  proteid  can  be  applied  to  meats,  wheat,  corn,  and  other  sub- 
stances. 

Test  for  carbohydrates.— Prepare  some  starch  paste  by  boiling  a  little 
corn-.starch  in  water.  Add  a  little  of  the  starch  to  a  test-tube  full  of  water  and 
shake  well.  Add  to  this  a  drop  of  the  tincture  of  iodine  and  the  liquid  will  turn 
blue.  This  is  a  test  for  starch,  and  may  be  applied  to  i:)otato,  flour,  and  other 
substances  containing  starch. 

Slow  and  rapid  oxidation.— The  experiment  alluded  to  in  the  text  of 
burning  magnesium  ribbon  is  performed  by  holding  a  piece  of  the  ribbon,  one 
or  two  inches  in  length,  with  pliers,  and  lighting  it  with  a  match.  The  light  is 
brilliant,  but  the  combustion  is  quiet  and  safe.  The  slow  combustion  is  similar 
to  what  is  called  rust  in  case  of  iron,  and  may  require  a  week  or  two. 

Heat  from  a  mixture  of  sulphuric  acid  and  water.— Fill  a  test- 
tube  or  small  bottle  half  full  of  water  and  j:)Our  into  it  slowly  about  the  same 
amount  of  strong  sulphuric  acid.  The  bottle  will  become  so  hot  that  it  cannot 
be  held  in  the  hand.  This  acid  must  be  handled  with  care.  To  carry  out  the 
illustration  suggested  in  the  last  paragraph  of  this  chapter,  add  some  carpet- 
tacks  or  small  pieces  of  iron  to  the  mixture  and  note  the  rapid  corrosion  of  the 
iron. 


CHAPTER    VTTI 


DIGESTION 


What  digestion  is.  -Digestion  of  food  is  a  process 
by  which  food  is  so  chang^ed  that  it  can  be  taken  into  the 
blood-vessels  of  the  bodj^  For 
example,  we  eat  a  great  deal  of 
starch,  bnt,  although  it  may  be  in 
the  stomach  or  intestines,  it  will  be 
of  no  benefit  to  the  body  as  long 
as  it  is  starch. 

The  starch  must  be  changed  to 
sugar  by  certain  juices  that  are 
poured  out  upon  it  in  the  intes- 
tines, and  the  sugar  is  then  easily 
dissolved  and  can  be  passed  through 
the  cells  in  the  wall  of  the  intes-  b 

tines  and  into  the  blood-vessels 
close  by.  Such  a  change  in  the 
character  of  food  is  called  diges- 
tion. 

Why    digestion    is    neces 

sary.-Food  must   not  only  be  in   j,^^    48.-Apparatus  to 
solution,  as  just  explained,  but  the    show  osmosis  of  liquids, 
solution  must  be  of  a  certain  kind. 

Most  of  it  gets  through  the  walls  of  the  intestines  by  a 
process  called  osmosis.  In  Fig.  48  is  shown  a  simple 
apparatus  to  illustrate  this  principle. 

95 


96  THIRD    BOOK    OF   PHYSIOLOGY 

A  is  a  vessel  partly  filled  with  water.  B  is  a  thistle 
tube,  over  the  bottom  of  which  is  tied  a  jjiece  of  any 
animal  membrane,  such  as  bladder  or  the  cjising  taken 
from  bologna.  B  is  then  partly  filled  with,  say,  a  strong 
solution  of  salt  and  suspended  in  the  water.  After  a 
time  the  liquid  in  B  will  rise  in  lieight  and  the  water  in 
A  will  become  slightly  salt.  This  shows  that  there  is  a 
movement  of  the  liquids  through  the  membrane  in  both 
directions,  but  more  rapidly  into  B.  In  the  apparatus 
shown,  copper  sulphate  was  used  in  the  tube,  and  the 
liquid  raised  from  the  point  .c  to  I  and  flowed  over  the 
top. 

Any  solutions  that  will  diffuse  into  each  other  will  pass 
through  such  a  partition,  when  placed  between  them, 
even  more  readily  than  without  it. 

While  the  food  is  in  the  intestine,  a  thin  sejjta  of  this 
kind  is  between  it  and  the  blood.  The  food  passes  through 
bj"  osmosis. 

After  the  food  is  carried  by  the  blood-vessels  to  the 
various  i)arts  of  the  body,  it  passes  out  to  the  cells  by  a 
similar  process.  Digestion  must  change  foods  to  a  solu- 
tion which  is  capable  of  this  kind  of  diffusion. 

The  fats  are  not  digested  in  this  manner,  but  they  get 
into  the  blood  by  being  passed  in  fine  droplets  through 
the  body  of  the  cells  that  line  the  intestines, — a  process 
not  yet  understood. 

The  alimentary  tract. — The  alimentary  or  digest- 
ive tract  may  be  considered  a  long  tube  through  which 
the  food  is  made  to  pass.    As  the  food  is  pushed  along,  it  is 


DICKS'HON  97 

acted  upon  by  tlie  various  dij^estive  lliiids,  wliicli  change 
it  to  a  condition  suitable  for  intro(hiction  into  the  body. 
While  tlie  food  is  in  the  tube  it  is  still  on  the  outside  of 
the  body  i)ro])er,  for  the  tube  is  only  an  op(uiing  through 
the  body.  Food  is  not  in  the  Inxly  until  it  is  taken  up 
by  the  blood. 

Tlie  entire  tract  is  lined  with  nuicous  membrane. 

The  parts  of  the  alimentary  tract  are  the  mouth,  fauces^ 
phanjnx\  oesophagus,  sfonlach,  small  intestines,  and  large 
intestines. 

The  mouth. — The  mouth  may  be  considered  the 
gateway  to  the  digestive  tract.  It  is  here  that  we  can 
exercise  our  will  as  to  the  kind  and  character  of  the  food 
which  we  will  take. 

After  food  is  swallowed,  digestion  is  carried  on  without 
any  attention  on  our  part.  In  the  mouth  occur  the  first 
two  acts  of  digestion.  These  are  mastication  and  insali- 
vation. 

Mastication.  The  teeth. — The  part  of  the  mouth 
concerned  in  the  first  step  in  digestion  is  the  teeth.  The 
front  teeth  bite  off  morsels  of  food  and  the  back  teeth 
grind  the  food  into  fine  bits. 

Since  the  proper  food  for  infants  is  milk,  teeth  do  not 

appear  until  about  the  age  of  six  months.     At  that  age 

a  temporary  set  of  teeth  begin  to  cut  through  the  gums 

one  after  another,  until  at  about  two  years  of  age  there 

are  ten  teeth  in  each  jaw. 

These  do  not  last  long,  for  soon  a  permanent  set  starts 

7 


98 


THIRD    BOOK    OF   PHYSIOLOGY 


beneath  tbeni,  and  at  the  age  of  five  or  six  years  l>egin  to 
push  out  the  first  set  and  to  take  their  phices.  At  the 
age  of  twelve  or  thirteen  years  all  the  permanent  teeth 
have  appeared  except  the  back  ones,  which  are  called 
wisdom  teeth,  and  which  do  not  come  till  the  age  of 
twenty  or  twenty -five  yeais. 


Fig.  49. — -Permanent  teeth  of  the  right  side.      (Gray.)     1,  2,  and  3, 
molars  ;  4  and  o,  bicuspids  ;  6,  canine  ;   7  and  8,  incisors. 

The  full  set  numbers  sixteen  in  each  jaw,  making  thirty- 
two  in  all.  In  each  jaw  the  four  front  teeth  are  called 
incisors ;  the  next  two,  one  on  each  side,  are  the  canines  ; 
the  next  two  on  each  side  are  hicuspids ;  the  last  three  on 
each  side  are  the  molars. 


Composition  of  teeth. — Teeth  are  made  of  a  hard 
material  similar  to  bone.  They  are  composed  of  a 
crown,  which  is  that  part  extending  beyond  the  gums ; 


DIGESTION 


99 


the  neck,  which  is  surrouiKh'd  by  the  <^uins  ;  and  the  yoot, 
which  is  einbe(hhMl  in  Ww,  hour  of  tlic  jaw  iind  liniily 
fixed  with  cement. 

A  cross- sec  Mo  11  of  a  tooth  shows  that  it  is  composed  of 
three  parts.  In  the  centre  is  the  i)iilp-cavity,  wliicli  is 
filled  with  a  nct-woi'k  of  blood-vessels  and  nerves. 


Fig.  50. — Longi- 
tudinal section  of 
tooth.  E,  enamel ; 
D, dentine;  P, pulp. 


Fig.    51. — Cross-section    of    tooth, 
masrnified,  sliowinsr  enamel. 


Surrounding  the  pulj)  is  the  dentine,  which  is  very 
hard,  and  yet  is  alive  and  composed  of  fibres  radiating 
from  the  pulp  and  receiving  nourishment  from  the  blood 
that  circulates  through  the  pulp-cavity. 

Enamel  covers  the  crown  of  the  tooth  and  is  thickest 
on  the  grinding  surface.  It  is  the  hardest  substance  in 
the  body,  and  can  withstand  a  great  deal  of  grinding 
without  wearing  away.  Fig.  51  shows  a  very  thin  sec- 
tion of  tooth  as  it  appeared  under  the  microscope. 


100  THIRD   BOOK   OF   PHYSIOLOGY 

Salivary  glands. — The  process  of  griDding  the  food 
between  the  teeth  is  called  mastication.  While  food  is 
being  masticated,  a  fluid  called  saliva  is  poured  out  into 
the  mouth  through  ducts  from  the  salivary  glands. 

There  are  three  sets  of  these  glands.  They  are  the 
parotid,  submaxillary,  and  subungual, — two  of  each  kind. 

The  parotid  glands  are  situated  just 
below  and  in  front  of  the  ears,  and 
the  ducts  from  them  open  into  the 
mouth  on  the  inner  surface  of  the 
cheek,  near  the  second  molar  tooth 
of  the  upper  jaw.  The  submaxillary 
\J^  ^  and   sublingual    glands    are    situated 

Fig.  52.— Racemose     beneath   the  tongue,  and  empty  into 
^       ■  the  mouth  just  under  the  tongue. 

These  are  called  racemose  glands,  because  they  consist 
of  sacks  all  connected  together  and  giving  the  whole 
the  appearance  of  a  bunch  of  grapes,  as  shown  in 
Fig.  52. 

The  purpose  and  nature  of  saliva. — The  office 
of  saliva  is,  first,  to  keep  the  mouth  moist  at  all  times ; 
second,  to  moisten  the  food  so  that  it  may  be  more  thor- 
oughly masticated  and  afterwards  swallowed  ;  third,  to 
dissolve  some  of  the  foods  that  are  already  soluble  ;  and, 
fourth,  to  begin  the  change  of  starch  to  sugar. 

Saliva  is  almost  pure  water,  but  it  contains  a  ferment 
called  ptyaliHj  which  causes  the  change  of  starch  to 
sugar. 

Ptyalin  is  not  a  living  organism,  like  a  yeast  ferment. 


DIGESTION  101 

It  can  chan<i:e  an  indefinite  quantity  of  starch  to  sugar 
without  itself  wasting  away,  and  so  only  a  small  quan- 
tity is  needed. 

The  "ropy"  cliaracter  of  the  saliva  in  the  mouth  is 
due  to  the  secretions  of  the  mucous  membrane  which 
lines  the  mouth. 

The  fauces. — After  the  food  has  been  masticated 
and  mixed  with  saliva,  it  is  pushed  by  the  tongue 
through  the  fauces, — an  opening  in  the  back  part  of  the 
mouth.  The  fauces  is  surrounded  by  the  soft  palate  and 
umda  above,  the  base  of  the  tongue  below,  and  pillars  of 
muscles  and  the  tonsils  at  the  sides. 

The  uvula  is  at  the  centre  above  and  hangs  lower  than 
the  soft  palate. 

The  tonsils  are  small  glands  that  secrete  mucus. 


The  pharynx. — After  i)assing  the  fauces  the  food 
reaches  the  pharynx.  The  pharynx  is  a  centre  for  a 
number  of  passages  which  radiate  from  it.  It  is  some- 
what conical  in  shape,  with  the  small  end  downward. 

From  it  are  seven  openings :  one  into  the  larynx, 
leading  to  the  lungs  ;  one  into  the  gullet,  leading  to  the 
stomach ;  one  into  the  mouth  :  two  into  the  nostrils ; 
two  into  the  Eustachian  tubes,  communicating  with  the 
drums  of  the  ears. 

At  the  top  of  the  windpipe  is  a  plate  of  cartilage 
called  the  epiglottis.  This  is  raised  during  breathing, 
but  shuts  down  like  a  lid  when  food  is  being  swallowed. 


102  THIRD   BOOK   OF   PHYSIOLOGY 

The   epiglottis   can   be   seen    if   the    mouth   be   widely 
opened  and  the  tongue  pressed  down. 

The  oesophagus.  Deglutition.— The  oesophagus 
is  a  tube  leading  from  the  pharynx  down  through  the 
chest  to  the  stomach.  It  lies  near  the  spinal  column,  and 
at  its  lower  end  it  pierces  the  diaphragm  and  enters  the 
stomach  just  beneath.  It  is  composed  of  two  layers  of 
muscle,  the  fibres  of  one  running  lengthwise,  and  of  the 
other  around  the  tube.  It  is  lined  with  mucous  mem- 
brane. 

After  food  has  once  entered  the  oesophagus  it  is  forced 
down  by  an  involuntary  contraction  of  the  muscles  just 
above  it.  It  is  not  possible  to  perform  the  act  of  swal- 
lowing unless  there  is  something  to  swallow,  as  may  be 
shown  by  swallowing  three  or  four  times  in  quick  suc- 
cession, until  all  saliva  is  removed  from  the  mouth. 

The  act  of  swallowing  is  called  deglutition. 

The  stomach. — The  stomach  may  be  considered  a 
place  where  the  alimentary  tract  is  expanded  into  a 
pouch.  Here  the  food  is,  for  a  time,  arrested  in  its 
progress  along  the  tract. 

The  stomach  is  situated  on  the  left  side  of  the  body, 
just  beneath  the  heart.  When  fairly  well  filled  it  is 
about  ten  inches  long  and  five  inches  through  its  widest 
part.  It  has  two  openings.  One  is  called  the  cardiac 
orifice,  where  the  food  enters,  Fig.  53,  c.  The  other  is 
called  the  xyyloruH,  ]).  A  ring  of  muscle  about  the  pylorus 
keeps  it  closed  except  when  food  is  ready  to  pass  through 


hlCKS'PIoN 


103 


it.  Tlio  stoiuacli  lias  foiir  <'();its,  ('all('(l  Uk^  srrons  (see 
page  20),  the  musculcir,  tlic  (trcolar  (see  page  2()),  and  the 
viucoun.  The  bust  naiiKMl  is  the  coat  next  to  the;  contents 
of  th(;  slomacli. 


Fig.  53. — Stomach  and  intestines. 


The  mnscular  coat  is  composed  of  three  layers.  In 
the  outside  one  the  fibres  run  lengthwise,  in  the  next 
they  pass  around  the  stomach,  in  the  third  the  fibres 
radiate  obliquely  from  the  cardiac  orifice,  but  do  not 
form  a  complete  layer. 

The  peritoneum  (see  page  30)  suspends  the  stomach  as 


104  THIED    BOOK    OF    PHYSIOLOGY 

in  a  sling,  and  between  its  folds  blood-vessels  run  to  the 
stoniacli. 

The  mucous  coat. — ^The  mucous  coat  is  the  most 
important  of  the  four  coats  of  the  stomach.  When  ex- 
amined with  a  microscope  of  only  moderate  power  it  is 
seen  to  have  a  honeycomb  appearance,   caused  bj'  the 


Fig.  54. — Mucous  coat  of  stomach,  epithelial  layer  removed,  showing 
the  openings  of  the  gastric  glands. 

minute  shallow  pits  that  cover  its  surface.  In  each  pit 
is  the  mouth  of  a  gastric  gland.  These  glands  are  minute 
tubes,  packed  in  between  the  columnar  epithelium  cells. 
(See  page  24.)  They  secrete  the  gastric  juice  which 
effects  the  stomach  digestion. 

Digestion  in  the  stomach.— While  the  food  is 
being  masticated  the  gastric  juice  is  being  secreted  and 
poured  out  into  the  stomach,  ready  for  the  food  when  it 
arrives.     Secretion  of  gastric  juice  continues  during  di- 


DKJESTIOX  105 

gestion.  The  saliva  is  an  alkaline  substance,  but  gjistiic 
juice  is  str()ni::ly  acid  in  its  reaction,  so  that  the  conver- 
sion of  starch  to  sujjjar  by  the  saliva  ceases  while  the 
food  is  in  the  stomach. 

Gastric  juice  is  composed  of  pepsin,  rennin,  coaler,  and 
about  .2  per  cent,  of  hydrochloric  acid. 

The  pepsin  converts  the  proteids  mto  peptones,  and  in 
that  condition  they  can  pass  by  osmosis  through  the 
membranes  that  line  th^  alimentary  tract. 

The  rennin  coagulates  the  casein  of  milk  and  the  pep- 
sin then  converts  it  also  to  peptone. 

The  starches  are  not  changed  in  the  stomach. 

The  albuminous  walls  of  the  fat  cells  are  dissolved 
away,  but  the  fat  is  not  changed. 

The  presence  of  food  stimulates  the  muscular  walls  of 
the  stomach  to  action.  By  their  alternate  contraction 
and  relaxation  they  i^roduce  a  movement  called  peri- 
staltic motion.  By  this  means  the  contents  of  the  stomach 
are  moved  about  and  thoroughly  mixed  together. 

The  mass  of  food,  after  it  has  been  digested  in  the 
stomach  for  some  time,  is  of  about  the  consistency  of 
thick  cream,  and  is  called  chyme. 

From  time  to  time,  as  the  digestion  of  the  proteids 
is  completed,  the  pylorus  opens  and  lets  the  chyme 
through.  In  from  two  to  four  hours  the  stomach  is 
empty  again. 

The  small  intestine. — The  small  intestine  is  about 
twenty  feet  in  length,  though  varying  considerably  in 
different  persons.     It  begins  at  the  pyloric  orifice  of  the 


106  THIRD   BOOK   OP   PHYSIOLOGY 

stomach,  wheie  it  is  largest,  and  ends  at  the  large  intes- 
tine. The  first  ten  inches  of  it  is  called  the  duodenum 
(twelve)  because  it  is  about  as  long  as  twelve  fingers 
placed  side  by  side.  The  next  eight  feet  of  it  is  called 
the  jejunum  (emptjO-  The  remainder  is  called  the  ileum 
(twisted)  because  of  its  many  folds. 

Like  the  stomach,  the  small  intestine  is  composed  of 
four  coats, — the  serous^  muscular,  areolar,  and  mucous. 

The  serous  coat  is  formed  by  folds  of  the  j)eritoneum. 
These  folds  are  called  the  mesentery,  and  they  serve  both 
to  support  the  intestines  and  to  conduct  the  blood-vessels 
to  them. 

The  muscular  coat  has  two  layers,  one  running  length- 
wise and  the  other  being  circular.  The  circular  is 
stronger  and  of  more  importance. 

The  mucous  coat. — The  mucous  coat  of  the  small 
intestine  lies  in  the  permanent  folds  or  ridges  called 
valvulce  conniventes  which  pass  transversely  around  the  in- 
testines. They  prevent  a  too  rapid  passage  of  food  along 
the  intestine  and  present  a  larger  surface  for  absorption. 

On  the  inner  surface  of  the  mucous  coat  are  small  pro- 
jections called  villi.  These  are  only  about  tV  of  an  inch 
long,  but  they  stand  close  together,  giving  the  surface  a 
velvety  appearance.  In  Fig.  55  is  shown  a  section  of 
the  small  intestine  of  a  cat.  As  the  section  is  very  thin 
and  is  magnified,  the  villi  do  not  have  their  natural, 
crowded  appearance. 

In  Fig.  56  is  shown  a  few  villi  of  the  same  specimen 
as  above,  but  more  highly  magnified.     The  dark   lines 


DK.'KSTION^ 


lo: 


show   th»*   blood-vessels,    wliicli    ure    liere   filled    with   a 
colored  sui)stunce. 


j^ 


''> 


/ 


Fio.  5-3. — Section  of  smaii  mrostine  of  cat. 

A^Tien  a  villus  is  clos^^ly  examined,  it  is  fonnd  to  be 
covered  with  a  layer  of  epithelial  cells  as  shown  in  Fig.  57. 


FiG.  56. — Micn)photograph  of  villi. 

Within  is  a  net-work  of  ves.sels  to  receive  and  carry  away 
the  liquids  that  pass  through  the  layer  of  cells.     In  the 


108 


THIRD   BOOK   OF   PHYSIOLOGY 


centre,  L,  is  a  tube  called  a  lacteal,  which,  during  diges- 
tion, is  filled  with  a  milky  white  liquid.  About  the 
lacteal  are  the  capillary  blood-vessels. 

Here  and  there  between  the  villi  are  the  mouths  of 
glands  called  the  crypts  of  Lieberkiihn. 


Fig.  57. — Diagram  of  villus.     E,  layer  of  epithelial  cells  ;  yl,  artery 

F,  vein  :   L,  lacteal. 


The  liver. — Two  large  glands  concerned  in  intestinal 
digestion  are  set  off  from  the  alimentary  tract,  but  con- 
nect with  it  by  means  of  ducts,  through  which  they  pour 
their  secretions  into  the  small  intestine.  These  glands 
are  the  liver  and  the  pancreas. 

The  liver  is  the  largest  gland  in  the  body  and  weighs 
from  three  to  four  pounds.  It  is  situated  on  the  right 
side  of  the  abdomen,  just  below  the  diaphragm,  and 
consists  of  five  lobes.  It  contains  a  net-work  of  tubes, 
through  which  the  blood  and  other  liquids  circulate. 


DKiKSTloX 


100 


Fig.  58.— External  view  of  liver.  1,  riglit  Icbe  ;  2,  left  lobe;  ^, 
portal  vein;  4,  hepatic  artery;  o,  bile  duc-t ;  6,  gall-bladder;  7,  in- 
ferior vena  cava. 


Fig.  59.— Lobule  of  the  liver.  Blood  is  brought  by  portal  vein  to 
outer  surface  of  the  lobule  and  flows  through  the  lobule  to  its  centre, 
where  it  is  collected  by  the  hepatic  vein  and  conducted  to  the  inferior 
vena  cava. 


110  THIRD    BOOK   OF  PHYSIOLOGY 

On  close  examination  it  is  seen  that  the  liver  is  made 
up  of  a  great  number  of  masses  called  lobules.  Each 
lobule  consists  of  hepatic  or  liver  cells,  between  which 
run  numerous  fine  blood-tubes.  The  work  of  the  liver 
is  done  by  these  cells.  In  Fig.  59  is  seen  a  cross-section 
or  a  lobule  highly  magnified. 

The  liver  is  of  great  service  to  the  body  in  sevei'al 
ways.  In  this  chapter  we  are  interested  in  its  ability 
to  produce  bile.  This  substance  is  gathered  up  by  nu- 
merous hepatic  ducts,  which  finally  unite  and  pour  the 
bile  into  the  duodenum. 

Beneath  the  liver  is  a  gall-bladder,  in  which  the  gall  is 
stored  when  not  needed  for  digestion. 

The  pancreas. — The  other  large  gland  concerned  in 
digestion  is  the  pancreas.  It  is  situated  in  the  abdomen 
back  of  the  stomach.  It  is  a  racemose  gland  and  re- 
sembles those  that  secrete  saliva.  It  is  six  to  eight 
inches  long,  but  quite  narrow  and  thin,  weighing  only 
from  two  to  four  ounces. 

Its  function  is  to  secrete  pancreatic  juice,  which  is 
poured  through  a  duct  that  opens  into  the  bile  duct  just 
before  it  reaches  the  duodenum. 

Digestion  in  the  small  intestine.— While  the 
food  is  passing  through  the  process  of  gastric  digestion, 
the  glands  concerned  in  intestinal  digestion  secrete  their 
juices  and  pour  them  into  the  small  intestine.  When 
the  chyme  passes  through  the  pj^lorus  into  the  duo- 
denum,  digestive  juices  are  there   ready  to  receive  it. 


DIGESTION  111 

These  are  the  pancreatic  juice,  the  bile,  ami  the  secre- 
tions from  the  small  glantLs  embedded  in  the  niucx)us 
coat  of  the  intestine. 

These,  when  mingled  with  tln'  food  nuuss,  change  the 
acid  chyme  to  tlic  iilkaliiR'  chiile. 

Action  of  the  pancreatic  juice.— The  secretion 
of  the  paucrea^s  is  the  most  important  of  the  intestinal 
juices.  It  is  a  clear,  alkaline  liquid,  and  is  capable  of 
doing  three  things  :  First,  it  rapidly  converts  starch  into 
sugar.  This  action  was  begun  by  the  saliva,  but  was 
stopped  by  the  acid  in  the  gastric  juice  of  the  stomach. 

Second,  it  digests  any  proteids  that  escaped  digestion 
in  the  stomach. 

Third,  it  changes  some  of  the  fats  to  soap,  in  which 
form  it  is  soluble  in  water,  and  so  can  be  absorbed. 
Most  of  the  fats,  however,  lue  only  emulsified,  and  are 
passeil  as  small  droplets  through  the  bodies  of  the  epi- 
thelial cells. 

The  action  of  bile. — The  human  bil«.'  i.s  a  brownish 
liquid,  but  will,  if  kept  for  a  time,  turn  green.  Its  use 
is  not  fully  known,  but  it  is  certain,  from  the  bad  etfects 
which  follow  when  the  supply  is  shut  off,  that  bile  has 
an  important  office  in  digestion. 

It  is  alkaline,  and  helps  to  neutralize  the  acid  of  the 
chyme.  It  excites  the  muscular  coat  to  action,  and  tlius 
is  a  means  of  moving  the  food  along  the  intestine. 

It  also  facilitates  the  absorption  of  fats. 

Intestinal  juice. — The  juice  secreted  by  glands  in 
the  mucous  coat  of  the  intestine  is,  like  the  other  two, 


112  THIRD    BOOK   OF    PHYSIOLOGY 

alkaline.     It  converts  the  sugars   which  we  eat  into  a 
kind  which  can  be  more  readily  absorbed  by  the  villi. 


The  large  intestine. — The  final  portion  of  the  ali- 
mentary tract  is  called  the  large  intestine.  It  is  but  five 
feet  in  length,  but  is  called  ''large"  because  it  will  aver- 
age about  two  inches  in  diameter.  The  area  of  its  cross- 
section,  then,  is  nearly  four  times  as  great  as  that  of  the 
small  intestine. 

It  begins  on  the  right  side  of  the  abdomen  and  ex- 
tends up  along  that  side,  forming  the  ascending  colon; 
then  across,  forming  the  transverse  colon;  then  down  on 
the  left  side,  forming  the  descending  colon.     (See  Fig.  53.) 

The  small  intestine  opens  into  the  side  of  the  colon 
some  distance  from  the  end.  At  this  opening  there  are 
folds  of  the  mucous  membrane  which  form  a  valve 
called  the  ileocolic  valve.  By  this  arrangement  the  con- 
tents of  the  small  intestine  may  easily  pass  into  the 
colon,  but  cannot  return. 

The  part  of  the  colon  below  the  ileocolic  valve  is 
called  the  cwcum  (blind),  because  it  is  closed  at  the  lower 
end.  From  the  caecum  hangs  the  vermiform  appendix. 
This  is  a  slender  tube  about  four  inches  long,  and  is  the 
seat  of  a  common  inflammation  called  apx^endicitis . 

The  coats  of  the  large  intestine  are  the  same  as  in  the 
small,  except  that  the  mucous  coat  is  not  supplied  with 
villi.     It  is  furnished,  however,  with  numerous  glands. 

Action  of  the  large  intestine.— By  the  time  the 
food  mass  has  reached  the  ileocolic  valve    its  valuable 


DKiESTION  113 

food  contents  have  been  largely  absorbed.  Tliat  which 
enters  the  colon  is  mostly  water,  some  food,  and  wiuste 
products.  In  the  large  intestine  a  great  deal  of  water  is 
absorbed,  and  the  digestion  of  the  remnants  of  fo(Kl  will 
continue  and  the  food  will  be  absorbed. 
The  residue  is  cast  from  the  body. 

Hygiene  of  Nutrition.  Mastication.— Thor- 
ough mastication  is  a  hiatter  of  real  importance  in  the 
preparation  of  the  food  for  digestion.  Foods  must  be 
chewed  until  they  are  thorough!}^  ground  up.  Experi- 
ments show  that  those  who  insist  on  thorough  mastication 
ha\e  fewer  ailments  of  their  digestive  organs  and  are 
stronger  with  a  less  quantity  of  food. 

Even  when  food  is  quite  soft,  it  is  necessary  to  chew  it 
until  it  is  well  mixed  with  saliva,  for  the  ferment  in 
saliva  continues  its  effect  on  starch  throughout  the  diges- 
tive tract,  except  in  the  acid  contents  of  the  stomach. 

Care  of  teeth. — Mastication  will  not  be  well  done 
unless  the  teeth  are  good.  Teeth  will  readily  decay. 
Particles  of  foreign  matter  allowed  to  remain  between 
the  teeth  is  the  cause  of  much  of  the  decay. 

After  each  meal  a  w^ooden  toothpick  should  be  used, 
and  the  teeth  washed  with  brush  and  water.  Since  the 
material  of  the  teeth  is  chiefly  phosphate  of  lime,  acid 
will  dissolve  them.  For  this  reason  it  is  well  to  use  often 
a  mild  soap  in  washing  the  teeth  to  neutralize  any  acid. 

Teeth  which  are  neglected  are  apt  to  become  covered 
with  a  coating  called  tartar.     This  is  not  only  injurious 


114  TIIIED   BOOK   OF   PHYSIOLOGY 

to  the  teeth,  but  objectionable  in  appearance,  and  should 
be  removed  by  a  dentist. 

Decay  begins  at  a  small  spot  on  a  tooth  and  extends 
in  to  the  pulp.  The  beginning  of  decay  may  escape  at- 
tention for  a  long  time,  and  after  toothache  begins  it  is 
often  too  late  to  save  the  tooth. 

It  is  a  good  plan  to  consult  a  dentist  two  or  three 
times  a  year,  if  only  to  be  assured  that  the  teeth  are  in  a 
sound  condition. 

A  healthy  stomach. — As  long  as  the  stomach  is  in 
a  healthy  state  one  is  seldom  conscious  that  he  has  such 
an  organ.  When  it  is  disordered,  however,  it  is  the 
cause  of  a  great  deal  of  suffering,  and  the  whole  body 
must  suffer  with  it. 

Some  practices  which  produce  a  disordered  condition 
of  the  stomach,  and  which  are  to  be  avoided,  are  :  (1) 
Eating  too  much  ;  (2)  forcing  food  into  the  stomach  be- 
fore it  is  properl}'  masticated  ;  (3)  eating  too  often,  thus 
keeping  the  stomach  constantly  excited  to  action  with- 
out periods  of  rest ;  (4)  doing  vigorous  work  either 
directly  before  or  after  a  meal ;  (5)  the  use  of  alcoholic 
drinks. 

When  proper  care  is  taken  with  respect  to  gastric 
digestion,  the  proper  conditions  for  the  best  intestinal 
digestion  will  be  provided  at  the  same  time. 

Alcohol  and  digestion. — It  was  once  customary  to 
take  at  meals  some  drink  containing  alcohol.  Some 
people  still  continue  the  custom.     It  was  supposed  to  aid 


DKIKSTKJxN  115 

digestion,  but  tests  nuidc,  in  i-et^ent  years  sliow  that  it 
retards  rather  than  promotes  digestion.  Food  w.ill  re- 
main longer  in  tlie  stomacli  when  alcohol  is  taken  with 
it.  Many  drinkers  are  troubled  with  catarrli  of  the 
stomacli.  The  mucous  membrane  becomes  inflanu^d  and 
unhealthy.  The  freedom  from  i)ain  which  the  dyspeptic 
experiences  after  a  drink  of  alcoholic  liquor  is  not  a 
result  of  the  curative  power  of  the  alcohol,  but  of  its 
deadening  eft'ect  upon  th'e  sensory  nerves. 

The  strong  appetite  which  some  have  for  strong  drink 
is  an  indication  of  a  disordered  condition  of  the  stomach. 
Appetite  for  bread  is  satisfied  whenever  enough  is  eaten, 
but  that  for  alcohol  may  increase  eveu  beyond  the  con- 
trol of  the  drinker. 

QUESTIONS  FOR   REVIEW. 

1 .  What  is  digestion  ?     Illustrate. 

2.  Why  is  digestion  necessary,? 

3.  Describe  an  experiment  showing  the  action  in  osmosis. 

4.  Have  ?/0M  tried  the  experiment? 

5.  How  do  fats  get  into  the  blood  ? 

6.  When  food  is  in  the  stomach,  is    it  inside    or  outside  the 
body  ?    Explain. 

7.  What  are  the  parts  of  the  alimentary  tract? 

8.  What  are  the  first  two  acts  of  digestion  ? 

9.  Describe  the  temporary  set  of  teeth. 

10.  Classify  the  permanent  teeth. 

11.  What  is  the  crown  of  a  tooth?    Name  the  other  parts. 

12.  AVhat  three  parts  are  observed  in  a  cross-section  of  a  tooth  ? 

13.  Describe  the  enamel.     The  pulp.     The  dentine. 

14.  How  is  saliva  secreted  ? 

15.  What  is  a  racemose  gland  ? 


116  THIED  BOOK   OF   PHYSIOLOGY 

16.  What  are  four  uses  of  saliva? 

17.  Whatisptyalin? 

18.  "What  makes  saliva  *'  ropy  "  ? 

19.  Bound  the  fauces. 

20.  What  is  the  uvula  ?     What  are  tonsils  ? 

21.  What  is  the  pharynx  ?    Name  the  openings  from  it. 

22.  What  is  the  epiglottis  ?     What  is  its  use  ? 

23.  What  is  deglutition  ? 

24.  Describe  the  cesophagus. 

25.  Locate  and  describe  the  stomach. 

26.  Describe  the  muscular  coats  of  the  stomach. 

27.  How  is  the  stomach  held  in  place? 

28.  Describe  the  mucous  coat  of  the  stomach. 

29.  What  are  the  digestive  juices  of  the  stomach  ?     What  is  the 
action  of  each  ? 

30.  What  kind  of  food  is  digested  in  the  stomach  ? 

31.  What  changes  are  made  on  fats  in  the  stomach  ? 

32.  AVhat  is  the  use  of  the  muscular  coats  on  the  stomach  ? 

33.  What  is  chyme? 

34.  Describe  the  small  intestine.     Name  its  parts. 

35.  What  is  the  mesentery  ? 

36.  What  are  valvulse  conniventes?    What  their  use? 

37.  What  is  a  villus  ? 

38.  Describe  the  structure  of  a  villus. 

39.  Describe  the  liver.     What  part  does  it  have  in  digestion  ? 

40.  Describe  a  liver  lobule. 

41.  Describe  the  pancreas. 

42.  What  three  juices  act  upon  the  food  in  the  small  intestine? 

43.  What  is  the  effect  of  the  pancreatic  juice  ? 

44.  What  is  the  use  of  the  bile? 

45.  Describe  the  large  intestine. 

46.  What  is  the  use  of  the  ileocolic  valve? 

47.  Describe  the  vermiform  appendix. 

48.  What  is  the  coecum  ? 


DKiKSTION  117 

49.  Describe  the  coats  of  the  colon. 

50.  "What  are  the  changes  on  the  food  in  the  colon  ? 

51.  AVliy  is  thorough  mastication  necessary? 

52.  What  causes  teeth  to  decay? 

53.  "What  are  some  ways  of  caring  for  the  teeth? 

54.  State  several  ways  by  which  the  stomach  maybe  disordered. 

55.  What  effect  does  cheerfulness  at  the  table  have  on  digestion? 
50.  What  effect  does  alcohol  have  on  digestion? 

57.  Will  alcohol  cure  the  cause  of  pain? 

58.  Why  does  appetite  for* alcohol  become  so  strong? 

59.  What  is  a  beverage?     (See  English  dictionary. ) 

EXPERIMENTS. 

To  illustrate  action  of  gastric  juice.— Prepare  an  artificial  gastric 
juice  by  mixing  together  pepsin  5  parts,  hydrochloric  acid  3  parts,  and  water  500 
parts.  Put  into  this  liquid  some  pieces  of  hard-boiled  egg,  and  keep  at  about  the 
same  temperature  as  the  body.  After  a  time  the  egg  will  be  dissolved,  or  digested. 
This  ilhistrates  digestion  of  proteids. 

Action  of  saliva. — Collect  one-half  test-tube  full  of  saliva  from  the 
mouth.  Put  iuto  it  a  little  cooked  starch  and  keep  warm.  In  a  short  time  make 
a  test  for  sugar  as  follows  : 

Add  to  the  contents  of  the  tube  a  few  drops  of  dilute  copper  sulphate.  Then 
add  caustic  soda  in  excess  until  the  liquid  becomes  a  clear  blue.  Now  boil  the 
liquid  in  the  upper  part  of  the  tube,  and  if  grape  sugar  be  present  it  will  turn  red. 

Emulsion  of  fats. — Shake  up  some  olive  oil  and  a  solution  of  caustic 
soda.  The  mixture  becomes  milky  in  appearance.  The  oil  is  divided  into  very 
fine  drops,  which  do  not  collect  together.     This  is  called  an  emulsion. 


CHAPTER   IX 

WHOLESOME   AND    UNWHOLESOME   DRINKS 

Much  of  the  ill-healtli  of  the  human  race  comes  from 
not  knowing  what  is  good  and  what  is  not  good  for  the 
body.  Untold  suffering  has  thus  resulted  from  ignorance 
concerning  the  nature  and  effects  of  alcoholic  drinks. 
Many  false  suppositions  concerning  their  origin  have  led 
to  mistaken  ideas  of  their  value.  It  is  very  important 
that  such  false  opinions  should  be  corrected. 

It  is  well  known  that  ripe  fruit  in  its  season  is  a  whole- 
some part  of  a  healthy  person's  diet ;  but  the  fruit  season 
in  the  temperate  zone  is  short,  hence  men  have  tried 
various  means  of  preserving  fruits  beyond  their  ripening 
time.  Drying  is  an  old  method  of  preserving  fruit.  In 
drying,  the  water  of  the  fruit  evaporates,  and,  if  care  is 
taken,  the  fruit  is  otherwise  not  much  changed. 

Another  way  of  preserving  fruit  is  to  boil  it  with  sugar 
and  seal  it  while  boiling  hot  in  air-tight  cans.  If  this  is 
well  done,  the  fruit  does  not  lose  its  wholesomeness.  But 
if  the  cans  are  not  perfectly  tight,  or  the  fruit  not  suffi- 
ciently heated,  germs  of  mould  or  other  minute  organ- 
isms get  inside  and  cause  the  fruit  to  spoil.  When  this 
happens  the  fruit  becomes  unfit  to  eat,  because  the  fer- 
mentation has  changed  its  nature.  It  is  apt  to  contain 
poisons  which  may  cause  illness  if  it  is  eaten. 
118 


wir()M-:s()Mi<:  and  rx\\Mi()r;i<:s()MK  dimxks  no 

Sometimes  people  wish  to  pieserve  only  the  juice  of 
fruit  and  use  it  iis  n  drink.  If  tlie  juice  is  pressed  out 
and  at  once  heated  and  sealed  in  air-tight  cans  or  bottles, 
while  boiling  hot,  it  can  be  kept  from  changing,  just  as 
fruit  can  by  canning.  If  the  juice  is  not  thus  heated  and 
bottled,  but  is  allowed  to  stand  after  it  is  pressed  out,  it 
will  soon  ferment  and  change.  During  the  fermentation 
a  poison  is  developed  which  makes  the  fermented  liquid 
unhealthful. 

The  cause  of  fermentation  in  expressed  fruit  juice  is  a 
small  germ,  invisible  except  under  a  microscope  ;  but  it 
is  not  the  same  kind  of  a  germ  that  causes  whole  or 
stewed  fruit  to  spoil.  The  germ  that  sets  up  fermenta- 
tion in  expressed  fruit  j  nice  is  a  species  of  yeast.  Similar 
germs  can  be  seen  in  common  yeast  by  soaking  it  and  ex- 
amining it  under  a  microscoi^e.  The  wild  yeast  germs 
float  in  the  air,  in  a  dry  state,  settle  upon  the  skins  and 
stems  of  fruit,  and  from  there  are  washed  into  the  juice 
when  it  is  expressed  from  the  fruit.  In  a  few  hours, 
under  the  right  conditions  of  moderate  warmth,  they 
begin  to  change  the  fruit  juice.  This  change  is  called 
alcoholic  fermentation,  because  the  sugar  of  the  fruit 
juice  is  thereby  changed,  in  whole  or  in  part,  to  alcohol 
and  carbon  dioxide  gas.  Every  fermentation  changes 
the  nature  of  the  substance  fermented. 

Fermented  fruit  juices  are  unhealthful^  because  they  con- 
tain alcohol,  which  is  a  poison  to  the  human  system. 

A  poison  is  any  substance  whose  nature  it  is  when 
absorbed  into  the  blood  to  injure  health  or  destroy  life. 
It  is  not  necessary  that  a  substance  cause  sickness  or 


120  THIED   BOOK   OF   PHYSIOLOGY 

death  at  once,  in  order  to  be  a  poison  ;  its  injurious 
effects  may  follow  so  slowly  and  subtly  that  they  do  not 
show  plainly  at  first. 

Poisons  are  classified  by  authorities  on  this  subject 
according  to  their  characteristic  effects  upon  the  body, 
or  its  various  i)arts.  A  narcotic  poison  is  one  that  dulls 
or  deadens  the  brain.  Alcohol  is  classed  by  writers  on 
poisons  among  the  narcotics,  because  its  most  important 
effect  is  to  dull  the  nervous  system.  It  is  similar  in  this 
respect  to  opium,  ether,  and  chloroform,  all  of  which 
belong  to  the  same  class,  i.e.,  narcotic  poisons. 

The  most  common  drinks  made  in  this  country  by  fer- 
menting fruit  juices  are  cider,  made  from  the  juice  of 
apples,  and  wine,  made  usually  from  the  juice  of  grapes, 
occasionally  from  currants,  elderberries,  and  some  other 
fruits. 

Wine  has  been  much  used  as  a  promoter  of  social 
intercourse.  The  narcotic  effect  of  the  alcohol  in  the 
wine,  when  only  a  small  quantity  is  taken,  dulls  the 
nerves  enough  to  take  the  edge  off  of  the  understanding 
and  weaken  the  self-control.  In  this  condition  a  person 
says  and  does  things  which  he  would  be  ashamed  of 
in  his  right  senses.  A  companj-,  after  the  effect  of  wine 
begins  to  show  itself,  will  laugh  at  silly  speeches  which 
at  other  times  would  seem  pitiable  instead  of  funny.  It 
is  a  poor  compliment  to  civilization  to  assume  that  people 
must  be  slightly  narcotized  before  they  can  be  agreeable 
companions. 

One  danger  in  social  wine  drinking,  in  some  classes  of 


WIIOLKSOME  AND  UNWHOLESOME  DRINKS    121 

society,  is  that  wine  lias  been  used  as  a  means  of  admin- 
istering drugs,  which  still  further  stupefy  the  iniud  and 
thus  quickly  i^repare  the  way  for  crime.  But  the  great- 
est danger  in  wine  is  the  power  of  the  alcohol  it  contains 
to  make  the  drinker  want  more,  while  it  destroys  the 
power  of  his  will  to  control  the  desire  for  more.  It  is 
futile  to  urge  self-control  in  the  use  of  a  substance  whose 
nature  it  is  to  destroy  self-control.  The  best  way  of 
exercising  self-control  in  regard  to  alcoholic  drinks  is  to 
refuse  the  invitation  to  take  them.  The  wine  drinker 
may  intend  to  be  moderate  ;  but  it  is  the  nature  of  the 
alcohol  in  his  wine  to  weaken  his  self-control  and  make 
him  immoderate. 

Light  wines,  such  as  are  ordinarily  used  as  beverages, 
contain  10  per  cent,  of  alcohol,  but  more  is  often  added 
to  wines  till  it  may  reach  as  much  as  35  per  cent. 

Cider  or  fermented  apple  juice.  The  juice  of 
apples  when  pressed  out  and  fermented  makes  a  liquid 
called  cider.  The  yeast  germs  which  are  on  the  surface 
of  the  api^les  when  they  are  ground  and  crushed  grow 
and  multiply  so  rapidly  in  the  exi^ressed  juice  that  in  a 
few  hours  much  of  the  sugar  of  the  juice  may  be  changed 
to  alcohol. 

Cider-making  is  a  common  way  of  disposing  of  small 
and  unsound  apples  ;  but  it  has  been  a  sad  economy  for 
many  farmers  whose  promising  sons  have  acquired  at 
the  cider-barrel  the  craving  for  alcohol  that  has  led  to 
their  destruction.  Hard  cider  contains  more  alcohol  than 
most  malt  liquors.      When  alcoholic  fermentation  has 


122  TIIIKD    BOOK    OF    PIITSTOLOGY 

gone  on  until  about  14  per  cent,  of  the  fermenting  liquid 
is  alcohol,  the  yeast  germs  can  no  longer  continue  their 
work.  Another  fermentation,  however,  the  acetic,  takes 
place  in  this  liquid  and  changes  the  alcohol  to  acetic  acid, 
by  which  process  hard  cider  is  turned  into  vinegar. 

Beer. — A  large  percentage  of  alcoholic  liquors  is 
made  from  grain  =  These  are  the  malt  liquors,  such  as 
beer,  ale,  and  porter,  which  may  contain  from  2  or  3  to 
10  per  cent,  of  alcohol.  The  most  common  of  these  is 
beer. 

One  of  the  x^rincipal  food  elements  in  grain  is  starch. 
When  grains  are  ground  and  made  into  flour  or  meal, 
and  then  into  bread  or  other  cereal  food,  the  starch  re- 
mains largely  unchanged,  except  such  i^arts  as  are  turned 
into  dextrine,  which  is  a  kind  of  sugar  and  a  good  food. 
When  grain  is  used  for  making  beer,  the  starch  is  first 
changed  to  sugar  by  sprouting  the  grain,  and  the  sugar 
is  then  soaked  out  with  water.  Thus  is  obtained  a  sweet 
liquid  called  wort,  the  sugar  of  which  can  be  changed  to 
alcohol  by  fermentation.  Yeast  is  added  to  the  wort. 
Alcoholic  fermentation  takes  place  and  changes  the  sugar 
of  the  wort  to  alcohol,  and  the  result  is  beer. 

Beer,  like  all  alcoholic  liquors,  is  a  dangerous  drink 
because  it  contains  alcohol. 

The  false  idea  that  beer  is  harmless  because  there  is  not 
much  alcohol  in  it  and  that  a  little  will  not  do  a  man  any 
harm,  is  a  cause  of  much  mischief.  It  makes  the  drinker 
careless  about  the  amount  he  drinks.  Even  if  he  takes 
but  little,  that  little  has  the  power  to  set  up  a  craving 


wrror.KsoMK  axd  t'xwitolesome  drinks  123 

for  more  that  leads  liim  to  make  uj)  for  tlie  weakness  of 
his  drink  bj'  the  quantity  lie  takes.  Thus  the  beer 
drinker  often  gets  as  much  alcohol  as  if  he  took  whiskey 
or  brandy. 

The  narcotic  effect  of  the  alcohol  further  deadens  the 
drinker's  sensibilities,  making  him  careless,  not  only 
about  his  own  welfare  but  that  of  others.  Judges  in 
criminal  courts  have  again  and  again  called  attention  to 
the  frequent  association  of  beer  drinking  with  the  com- 
mission of  crime.  Their  testimony  strengthens  the  evi- 
dence that  beer  is  a  demoralizing  drink. 

At  the  present  time  there  is  special  need  that  boys  be 
warned  against  the  offer  of  free  beer.  Accepting  such 
offers  may  fasten  upon  them  the  craving  for  alcohol  that 
will  lead  to  their  spending  the  most  of  their  future  earn- 
ings for  beer  or  other  alcoholic  drink.  The  effort  to 
teach  a  boy  to  drink  beer  is  not  made  for  the  benefit  of 
the  boy,  but  to  swell  the  number  of  beer  customers. 
Such  attempts  to  mortgage  a  boy's  future  money-earning 
power  to  drink  are  as  inhuman  as  the  bygone  i)ractice  of 
slave- catching  in  Africa. 

The  distilled  liquors,  gin,  whiskey,  rum,  brandy,  con- 
tain more  alcohol  than  the  fermented  drinks.  Gin  con- 
tains 38  per  cent.;  whiskey,  45  per  cent.;  rum,  48  per 
cent.;  brandj',  50  per  cent.  These  are  all  injurious  in 
proportion  to  the  amount  of  alcohol  they  contain. 

Drinking  water. — It  is  of  the  utmost  importance 
to  the  health  of  the  people  in  any  community  that 
only  good  drinking  water  be  used.     Water  is  the  only 


124  THIRD    BOOK    OF   PHYSIOLOGY 

drink  needed  by  man.  and  he  should  have  plenty  of  it 
and  have  it  free  from  impurities.  A  man  needs  about 
three  quarts  of  water  every  day.  A  part  of  this  is  already 
in  the  foods  eaten,  so  that  a  pint  or  more  of  water  as  such 
may  satisfy  the  body's  needs.  There  is  very  little  danger 
that  any  one  will  drink  too  much  pure  water.  A  gi'eat 
deal  is  needed  for  proper  digestion,  absorption,  secretion, 
and  excretion.  If  water  is  drunk  in  excess,  it  is  easily 
eliminated.  Most  people  drink  too  little  water.  It  should 
not  be  taken,  however,  to  moisten  the  food  in  the  mouth 
during  a  meal.     The  saliva  alone  must  do  that. 

Sources  of  water. — All  land  water  comes  from  rain. 
Part  of  it  remains  on  the  surface  in  rivers,  brooks,  pools, 
and  cisterns,  and  is  called  surface  water. 

Part  runs  down  through  the  ground  and  rocks,  thus 
supplying  the  springs  and  deep  wells.  Another  part  is 
just  beneath  the  surface  and  supplies  the  shallow  wells. 

Impurities  in  water. — Water  is  nature's  great  sol- 
vent, and  also  a  universal  culture  medium  for  all  kinds 
of  minute  organic  life.  While  it  slowly  percolates 
through  the  soil  and  rock,  it  takes  up  in  solution  many 
mineral  substances.  These  in  a  moderate  quantity  are 
not  objectionable.  Such  water  is  found  in  most  deep 
wells  and  springs. 

Surface  water  may  be  good  for  drinking,  but  it  is 
always  to  be  suspected. 

The  rain  falling  upon  the  land  carries  to  the  streams 
any  decaying  matter  which  may  be  Wiished  along,  and 


WIloT.FSO.MI-:  AND   IN  W  IIoI.ESOME  DRINKS   125 

the  sewage  of  a  city,  if  allowed  to  emptj'  into  a  stream, 
may  contaminate  the  water  with  germs  of  disease. 

Water  is  safe  only  when  free  from  decaying  matter. 
Shallow  wells  are  the  greatest  source  of  impure  water. 
Decaying  matter  from  barn-yards  or  out-houses  may  easily 
have  a  shallow  underground  i:)iissage  to  the  well. 


Fig.  60. — A  shallow  woll,  such  as  are  always  to  be  suspected. 

Such  wells  have  often  started  an  epidemic  of  typhoid 
fever.  A  painted  pumj:)  and  neat  lawn  and  curb  about 
such  a  well  do  not  purify  the  water,  for  the  poison  is 
seeping  in  beneath  the  surface. 

A  well  deep  down  into  the  rock,  with  water-tight  iron 
casing,  will,  as  a  rule,  contain  good  water. 


126  TIIirvD    BOOK    OF   PHYSIOLOGY 

Means  of  purifying  water.— Good  water  will  be 
without  color,  odor,  or  organic  matter  of  any  kind. 
Effort  is  often  made  to  provide  such  water  by  the  use  of 
small  house-filters.  These  may  make  the  water  clear,  but 
may  not  take  out  the  germs  of  disease  which  are  the  most 
objectionable.  In  fact,  an  old  filter  often  contaminates 
more  water  than  it  ever  purified. 

Nature's  way  is  to  filter  water  through  thick  layers  of 
clean  sand,  gravel,  earth,  and  rock,  thus  supplying  the 
deep  wells  with  pure  water.  This  cannot  be  done  for 
shallow  wells,  nor  can  man  imitate  this  method  on  a 
small  scale. 

Organic  matter  in  water  may  not  of  itself  be  injurious, 
but  may  be  a  food  for  certain  classes  of  germs  which  then 
grow  and  thrive  there. 

If  water  is  suspected,  it  should  be  boiled  (not  warmed) 
for  twenty  minutes.  This  will  efifectuallj'  destroy  all  bac- 
terial life  and  make  the  water  free  at  least  from  that 
danger. 

Ice  water. — The  custom  of  placing  ice  in  the  water 
to  be  drunk  is  a  wrong  practice  for  two  reasons. 

First,  if  the  water  was  impure  from  which  the  ice  was 
taken,  the  ice  will  be  impure.  Germs  of  disease  in  water 
are  not  killed  by  freezing  the  water. 

Second,  much  water  at  such  a  temperature  interferes 
with  digestion  and  may  produce  a  disordered  condition 
of  the  stomach. 

Water  may  be  cooled  by  ice,  but  the  melted  ice  should 
never  form  part  of  the  drinking  water. 


WIIOLKSOMI-:   AND    T  N  W  IIOLKSO.M  M    DIMNKS    127 

QUESTIONS   FOIl   KKVIKW. 

1.  lIoNv  may  fruit  be  presorvcd? 

2.  What  is  the  cause  of  feriiieiitatic.n? 

8.  Why  are  fermented  fruit  juices  unliealthful? 

4.  What  is  a  poison  ? 

5.  "What  kind  of  a  poison  is  alcoliol? 

0.  State  some  evil  effects  of  wine  drinking. 

7.  How  docs  the  juice  in  the  apple  differ  from  hard  cider? 

8.  How  is  beer  made  ? 

9.  State  some  of  the  evil  effects  of  beer  drinking. 

10.  What  are  distilled  liquors? 

11.  How  much  water  does  a  man  need  in  a  day  ? 

12.  What  is  the  effect  of  drinking  more  water  than  is  needed? 
i:].  Why  should  water  not  be  taken  along  with  foods? 

14.  What  becomes  of  the  water  which  falls  as  rain? 

15.  What  causes  water  to  be  "  hard"  ? 

16.  W' hy  is  rain  water  "  soft"  ? 

17.  What  is  the  source  of  impurities  in  water? 

18.  When  is  drinking-water  safe? 

19.  Explain  how  shallow  wells  are  liable  to  contain  impure  water. 

20.  Why  is  a  deep  well  better  ? 

21.  What  is  the  use  of  filters? 

22.  How  may  impure  water  be  made  fit  to  drink? 

23.  State  some  evil  results  that  may  follow  the  use  of  ice  water. 


CHAPTEE  X 

CIRCULATION 

Why  circulation  is  necessary.— We  have  seen 
that  the  body  is  made  up  of  a  g^reat  many  cells,  each 
having  a  life  of  its  own,  but  all  working  together  to 
serve  the  purpose  of  the  bodj^  as  a  whole.  All  the  cells, 
however,  except  the  white  corpuscle,  are  fixed  in  posi- 
tion and  incapable  of  moving  from  their  place. 

The  cells  cannot  live  without  food,  but  they  cannot  go 
after  it.  Circulation  of  the  fluid  food  is  necessary  to  carry 
nourishment  to  the  cells. 

The  cell  cannot  perform  its  functions  without  pro- 
ducing waste  products,  which  must  be  carried  away. 
Circulation  is  necessary  to  carry  off  waste  products  and  other 
objectionable  substances,  and  transport  them  to  organs  of  ex- 
cretion, such  as  the  lungs,  liver,  hidneys,  and  skin,  ichere  they 
may  be  taken  out  of  the  circulating  fluid  and  cast  from  the 
body. 

How  the  food  gets  into  the  stream  of  blood.— 

Under  the  subject  of  digestion  the  food  was  followed 
until  it  was  in  a  liquid  form  and  had  passed  through  the 
walls  of  the  villi  into  the  vessels  within. 

At   this   point  was  found   a   net-work   of  fine  tubes. 
These  are  a  part  of  the  general  circulating  system,  and 
here  the  food  is  taken  into  the  stream  of  blood.     Part 
128 


CIL'CCLA'no.V  129 

of  the  tubes  j^ather  u})  all  the  food,  except  the  fats,  and 
convey  it  to  the  liver.  Other  tubes,  calle<l  lacteals,  collect 
the  fats  and  convey  them  up  throuj^h  a  tube  called  the 
thoracic  duct  to  a  vein  in  the  left  shoulder,  whence  it  s<j(tn 
reaches  the  heart. 

The  blood  that  wius  carried  i'roni  the  stomach  and 
intestines  to  the  liver  was  there  changed  and  purified  by 
the  action  of  the  hepatic  cells,  and  thus  made  fit  to  be 
sent  out  to  the  other  cells  of  the  body. 

The  proteid  food,  as  has  been  explained,  was  changed 
by  digestion  to  peptone  so  that  it  would  dialyze  through 
to  the  blood-vessels  in  the  villi.  In  this  form  it  would 
be  a  poison  to  the  body,  and  must  be  changed  back  to 
proteid  again.  This  is  done  by  the  epithelial  cells  that 
cover  the  villi,  so  that  peptone  in  a  healthy  body  does 
not  get  into  the  circulation. 

Action  of  the  liver. — The  structure  of  the  liver 
and  its  office  in  the  secretion  of  bile  has  been  described 
on  page  108.  It  would  seem  strange,  however,  that  such 
a  large  gland  should  have  nothing  to  do  but  to  secrete 
bile.  It  appears  that  the  liver  has  another  duty  of  much 
greater  importance.  Its  chief  work  is  to  store  up 
glycogen  and  deal  it  out  to  the  current  of  blood  as  it 
is  needed. 

Glycogen  is  a  kind  of  sugar  which  the  liver  is  able  to 
make  from  the  sugars  that  are  eaten  and  the  starch  which 
was  converted  to  sugar  in  digestion.  The  quantity  of 
glycogen  in  the  liver  is  greatest  just  after  the  digestion 
of  a  meal  and  decreases   during   starvation   until   none 


130  THIRD    BOOK    OF   PHYSIOLOGY 

remains.  Thus  tlie  liver  acts  as  a  storehouse  of  this 
important  food. 

The  liver  is  also  a  door-keeper  guaiding  the  entrance 
of  food  into  the  circulation,  and,  within  the  limit  of  its 
ability,  will  take  out  substances  that  would  be  harmful 
to  the  system. 

After  food  passes  the  liver  it  is  carried  by  a  larj^e  vein 
to  the  heart. 

The  organs  of  circulation. — The  circulation  of 
the  blood  is  accomplished  by  means  of  the  heart.,  arteries., 
capillaries.,  veins.,  and  lymphatics.  The  heart  is  the  central 
organ  of  the  system,  and  from  it  pass  tubes,  through  some 
of  which  blood  is  sent  out.  and  through  others  blood  is 
received  back  again  to  the  heart. 

The  whole  system  of  tubes  through  which  the  blood 
circulates  is  closed  except  at  two  points,  where  the  lym- 
phatic ducts  enter  the  subclavian  veins, — one  on  each 
side  under  the  clavicle.  These  two  points  are  guarded 
by  valves  which  close  whenever  blood  would  flow  out 
into  the  ducts. 

There  is  no  place,  then,  where  the  blood  can  flow  out 
of  its  channel  to  other  tissues,  except  in  the  spleen  (see 
spleen),  and  so  the  food  can  get  to  the  cells  only  by  oozing 
through  the  walls  of  the  blood-vessels. 

This  occurs  only  in  the  capillaries.  The  jiurpose  of  the 
heart,  arteries,  and  veins  is  to  keep  the  capillaries  sup- 
plied with  a  fresh  current  of  blood. 

The  heart. — The  heart  is  a  large  hollow  bundle  of 
muscular  fibres.     It  weighs  ten  or  twelve  ounces.     It  is 


CIlJCrLATION 


131 


located  in  (lie  thorax  jnst  above  tlie  (liaplinjj^nn,  and 
midway  l)etween  tlic  rij^^ht  and  left  sides.  It  is  conieal 
in  shape,  witli  its  point  downward,  forward,  and  to  the 
left.  The  b;ise  of  the  heart  wonld  then  be  towards  the 
right  shonUler. 


^tT 


rr 


Fig.  61.  — External  view  of  the  heart.  1,  right  auricle;  2,  right 
ventricle;  3,  pulmonary  artery;  4,  left  auricle;  5,  left  ventricle;  6, 
aorta ;  7,  subclavian  veins ;  8,  carotid  arteries ;  9,  superior  vena 
cava  ;   10.  inferior  vena  cava  ;   11,  descending  aorta. 


It  is  enclosed  in  a  loose  bag,  which  is  attached  to  the 
diaphragm.  The  bag,  called  the  pericardium^  is  lined 
with  a  moist  and  very  smooth  serons  coat,  so  that  there 
is  very  little  friction  between  it  and  the  heart  proper. 


132 


THIRD    BOOK    OF    PHYSIOLOGY 


The  cavities  of  the  heart  are  also  lined  with  a  coat 
called  the  endocardiuni. 


Divisions  of  the  heart.— The  heart  is  double. 
The  two  halves  are  bound  together,  but  have  no  opening 

between  them.  They  are 
often  called  the  rigid  and 
left  hearts.  The  only  way 
blood  can  get  from  one  side 
of  the  heart  to  the  other  is 
by  going  out  in  a  circuit 
through  the  arteries,  capil- 
laries, and  veins,  and  then 
back  to  the  other  side. 

Each   side  of   the  heart 
contains  two  cavities.     The 
upper  ones  are  called  auri- 
cles and  the  lower  ones  ven- 
tricles.    So  there  is  a  right  auricle  and  a  right  ventricle  and 
a  left  auricle  and  left  ventricle:: 

The  left  side  of  the  heart  is  larger  and  stronger  than 
the  right. 

The  muscular  walls  of  the  left  ventricle  are  thick  and 
strong  because  they  have  the  most  of  the  heart's  work  to 
do, — that  of  forcing  blood  out  to  even  the  farthest  ex- 
tremity of  the  body. 


Fig.  62  — Diagram  showing 
cavities  of  the  heart.  RA^  right 
auricle  ;  R  F,  right  ventricle  ;  LA^ 
left  auricle  ;   L  F,  left  ventricle.  * 


Valves  of  the  heart. — ^Yhen  the  muscular  walls 
of  the  heart  contract  they  will  make  the  cavity  smaller 
and  the  blood  will  be  forced  out.     There  would  be  no 


riKrr'L  ATiox 


13.3 


advantajxc  in  tliis  if  tlie  blood  could  go  back  throun^h  the 
sjuiu'  tulM'  in  wbicli  it  oiitcrod  ;  so  valves  are  needed  to 


Open 


Closed 


Fio.  63.  —  Diagruiii  illustruting  the  action  oi  the-  auiiculu-veiitricular 

valves. 


Fig.  64. — Section  of  the  right  auricle  and  right  ventricle  of  the  heart. 

keep  the  blood  alwaj^s  flowinfij  in  the  same  direction. 
Between  the  auricles  and  ventricles  are  valves  having 
the  common  name  auriculo-ventricular   valves.     The  one 


134 


THIRD   BOOK   OF   PHYSIOLOGY 


between  the  right  auricle  and  ventricle  is  called  the  tri- 
cuspid  valve,  while  the  corresponding  one  in  the  left  heart 
is  called  the  mitral  valve.  These  valves  are  simply  flaps 
of  the  endocardium,  the  tricuspid  having  three  flaps  or 
cusps,  as  the  name  indicates,  and  the  mitral,  two.  These 
offer  no  resistance  to  blood  flowing  from  the  auricles 
into  the  ventricles,  but  any  attempt  of  blood  to  flow  in 
the  opposite  direction  would  push  one  flap  against  the 
other  and  thus  close  the  opening. 

Strong  cords  of  connective  tissue  are  fastened  to  the 
edge  of   the   flaps   and  to   the   walls  of  the   ventricle. 

These  permit  the  valves  to  close, 
but  prevent  their  going  any  far- 


ther. The  arrangement  is  sim- 
ilar to  that  of  double  swinging 
doors  which  open  in  only  one 
direction. 

At  the  point  where  the  blood 
is  forced  from  the  left  ventricle 
into  the  large  artery,  called  the 
aorta,  are  three  semilunar  valves. 
They  get  their  name  from  their 

half-moon  shape,  as  seen  in  Fig.  65.     They  open  to  blood 

flowing  out,  but  are  closed  by  any  movement  of  blood  in 

the  opposite  direction. 

The   same  arrangement  is  found  at  the  point  where 

blood  is  driven  from  the  right  ventricle  into  the  artery 

leading  to  the  lungs. 


Semilunar  valves 


Course  of  the  blood  in  the  heart.— The  blood 
enters    the    right    auricle   of    the   heart    and    flows    on 


CIRCULATION 


135 


Uiroii<^li  the  ti'icuspid  valve  into  the  rij^ht  ventricle. 
Wlieii  the  rij^^ht  veiitride  is  filled  its  muscles  contract 
and  squeeze  upon  tiic  hhMxl.  tlius  closing  the  tricuspid 
valve  and  forcing  the  blood  through  the  semilunar 
valves,  m  (Fig.  66),  into  the  artery,  S,  which  leads  to 
the  lungs. 


Fig.  go. — Diat!;rain  showing  the  course  ot  the  blood  through  the 
heart,  c,  superior  vena  cava  ;  />,  inferior  vena  cava  ;  Z),  right  auricle  ; 
e,  tricuspid  valve  ;  G  right  ventricle  ;  w,  semilunar  valve  ;  S,  pulmo- 
nary artery  ;  /j,  />,  />,  j),  pulmonary  veins  ;  A",  left  auricle  ;  /f,  left  ven- 
tricle ;   ?2,  semilunar  valve  ;   A,  aorta. 


When  the  blood  returns  from  the  lungs  it  enters  the 
auricle  on  the  left  side,  K,  and  passes  on  into  the  left 
ventricle,  H.  The  contraction  of  the  strong  muscles  of 
the  left  ventricle  closes  the  mitral  valve,  i,  and  forces 
the  blood  out  into  the  great  artery.  A,  which  carries  it 
to  all  parts  of  the  system. 


13G 


THIED   BOOK   OF   PHYSIOLOGY 


Thus  the  auricles  act  as  reservoirs  to  hold  the  blood 
while  the  valves  are  closed,  and  the  valves  act  like  the 
valves  of  a  pump,  opeuing  only  to  a  flow  in  one  di- 
rection. 

The  arteries. — Arteries  are  tubes  through  which 
blood  is  forced  out  to  the  various  tissues  of  the  body. 
The  arteries  stand  open  like  a  heavy  rubber  tube, 
whether  they  are  filled  with  blood  or  not. 


Fig.  67. — Section  of  arterv  and  vein.     A,  arterv  ;    V.  vein. 


The  walls  of  arteries  are  composed  of  three  coats. 
The  inner  one  is  thin  and  transparent,  being  a  continua- 
tion of  the  inner  lining  of  the  heart.  The  middle  coat 
is  quite  thick  in  the  larger  arteries,  and  is  composed  of 
muscular  fibres  and  yellow,  elastic  tissue  arranged  in 
rinsrs  around  the  tube.     The  outer  coat  is  composed  of 


(MIJCrrvATlOX  137 

layei's  of  wliitc,  fibrous  tissiu',  and  so  is  very  stroii<^  siiul 
U)Uii;h. 

Distribution  of  arteries. — The  arteries  arise  from 
the  iH'art,  one  from  each  ventricle. 

The  one  from  the  right  ventricle  carries  the  impure 
blood  to  the  lungs.     It  is  called  the  pulmonary  artery. 

The  one  from  the  left  ventricle  carries  the  pure  red 
blood  out  to  all  parts  of  the  body.     It  is  called  the  aorta. 

The  aorta  arches  up  over  the  heart,  sending  off 
branches  to  the  heart  itself  the  head,  and  the  arms. 
Then  it  descends,  close  to  the  backbone,  through  the 
thorax,  sending  off  numerous  small  branches  to  nourish 
the  tissues  in  that  region.  Then  it  passes  through 
the  diaphragm  into  the  abdomen,  where  many  large 
branches  are  distributed  to  the  important  organs  located 
there. 

Near  the  base  of  the  abdomen  the  aorta  divides,  one 
branch  passing  down  each  leg. 

Each  of  these  numerous  branches  also  divides  in  a 
similar  manner  until  the  tubes  are  so  small  they  cannot 
be  traced  except  by  the  aid  of  a  microscope.  At  the 
ends  of  the  numerous  fine  arteries  the  capillaries  begin. 

Capillaries. — The  capillaries  are  very  fine  tubes  that 
pervade  nearly  every  tissue  of  the  body.  They  are  in- 
terposed between  the  ends  of  an  artery  and  the  begin- 
ning of  a  vein. 

The  walls  of  the  capillary  tubes  are  an  extension  of 
only  the  thin  inner  layer  of  the  artery,  and  so  the  food 


138 


THIRD   BOOK   OF   PHYSIOLOGY 


contents  of  tlie  blood  can  easily  transfuse  to  the  cells  just 
outside. 

The  average  size  of  the  capillaries  is  about  xsVo  of  an 
inch,  but  they  lie  so  close  together  and  are  so  numerous 


Fig.  68. — Capillaries.     A,  terminal  of  fine  artery ;    V,  origin  of  vein. 

that  it  is  hardly  possible  to  prick  the  skin  with  a  fine 
needle  without  puncturing  some  of  them  and  letting  out 
some  blood. 

The   capillaries   are    the   most   essential   part    of    the 
whole  system  of  circulation,  for  it  is  from  them  alone 

that  the  cells  are  fed.  In  Fig. 
69  is  a  representation  of  the 
relation  of  the  capillaries  to  a 
bundle  of  muscle-fibres. 

The  cells  of  the  muscle  are 
surrounded  by  a  liquid  called 
lymph.  As  the  blood  passes 
through  the  capillaries  the 
cell-food  transfuses  through  into  the  lymph.  Both  the 
cells  and  the  capillaries  are  bathed  in  lymph,  and  the 
exchange  takes  place  according  to  the  principle  of  os- 
mosis explained  on  page  95. 

The  cell  then  takes  its  food  from  the  lymph. 

Blood   moves    very    slowly   in  the   capillaries, — only 


Fig.  69. — Diagram  showing 
muscle-cells  and  blood  capil- 
laries. 


CIRCULATION  139 

about  one  iiicli  in  ii  ininulc, — and  so  there  is  time  lor  the 
osiiiot  i(-  act  ion. 

Veins. — Tlic  arteries  lM'<xin  as  a  sinnle  laryc  I  nix*, 
which  (livi(h\s  and  snhdivides  until  the  hranclies  are 
exceedin<;iy  nnincrons  and  minute,  when  they  pass  into 
the  capillaries. 

At  the  other  end  of  each  capillary  is  a  minute  vein 
which  now  receiv(is  the  blood. 

These  fine  veins  unite  to  form  a  larger  tube,  which  in- 
cre;uses  in  size  as  it  approaches  the  heart. 

Thus  the  blood  flows  from  the  large  artery  out  to  its 
branches ;  while  in  a  vein  it  starts  at  the  branches  and 
is  collected  into  a  large  vein. 

The  arteries  distribute  blood,  the  veins  collect  it  and 
bring  it  back  to  the  heart  again. 

Two  large  veins  return  the  blood  from  the  system  to 
the  heart.  One,  called  the  superior  vena  cava,  collects  all 
blood  from  parts  above  the  heart,  and  another,  called  the 
inferior  vena  cava,  collects  all  blood  from  regions  below 
the  heart. 

Structure  of  veins. — The  walls  of  veins  are  com- 
posed of  three  coats  similar  in  structure  to  those  of  ar- 
teries, but  the  middle  one  is  not  uearly  so  thick.  Veins 
do  not  stand  open  except  when  filled  with  blood. 

In  the  veins  at  intervals  are  placed  semilunar,  or  half- 
moon,  valves,  at  some  points  one,  and  at  others  two  or 
three,  together.  They  are  pockets  fastened  to  the  walls 
of  the  vein  so  that  blood  may  floM'  past  them  towards 


140  THIRD    BOOK    OF   PHYSIOLOGY 

tlie  heart:  but  if  it  flows  in  the  opposite  direction  the 
pockets  will  fill  with  blood  and  press  a^^ainst  each  other, 
thus  closing  the  vein.  The  semilunar  valves  of  the  heart 
operate  in  the  same  way.     (See  Fig.  65.) 

Veins  are  slightly  enlarged  at  the  points  where  valves 
are  placed.  If  the  flow  of  blood  in  a  surface  vein  be 
stopped  by  pressure,  the  position  of  the  valves  can  be 
located  by  the  ••knots"  seen  here  and  there  along  the 
vein. 

Lymphatics. — As  explained  above,  the  active  tissue- 
cells  are  constantly  bathed  in  lymph,  which  is  constantly 
supplied  from  the  blood.  When  the  lymph  has  served 
its  purpose  it  must  bediained  off.  This,  however,  is  not 
done  by  the  veins,  but  by  a  special  system  of  tubes  called 
lymphatics.  These  begin  as  very  small  tubes  which  unite, 
forming  two  ducts  that  convey  the  lymph  to  the  right 
and  left  subclavian  veins. 

The  ducts  are  supplied  with  valves  similar  to  those  in 
veins. 

The  two  ducts  are  called  the  thoracic  duct  and  the  right 
lymphatic  duct. 

The  thoracic  duct  collects  the  lymph  from  the  lower 
extremities,  the  abdominal  organs,  the  left  side  of  the 
head  and  thorax,  and  the  left  arm.  and  empties  into  the 
left  subclavian  vein. 

The  right  lymphatic  duct  collects  from  the  right  side 
of  the  head  and  thorax  and  the  right  arm,  emptying  into 
the  right  subclavian  vein. 

The   thoracic   duct   also   receives   the  emulsified   fats 


riRcri-ATION  141 

whicli  were  coUccUmI  hy  the  lacteals  in  the  villi  of  tlie 
iiitesliiies- 

Lympliatic  nodes.  At  many  points  alonj^  tlie 
lymphatic  ducts  arc  iMxh's  or  knots.  Tli(iy  arc  imincrous 
in  the  ji;roins,  iicck,  anii[)its,  and  mesentery.  When  for 
any  reason  they  are  inflamed,  th^y  are  spoken  of  as 
'•waxen  kernels."  They  are  made  up  of  interlacing 
connective  tissue  packed  with  cells  which  are  \'(;ry  much 
like  white  corpuscles. 

The  lymph  filters  through  the  nodes,  carrying  witii  it 
some  of  the  cells,  which  become  white  corpuscles  in  the 
blood. 

The  spleen. — The  spleen  may  be  considered  a  large 
lymph-node.  It  lies  just  below  the  stomach  on  the  left 
side.  It  is  a  dark  red  body  about  five  inches  long  and 
weighs  about  six  ounces.  It  is  spongy  in  texture,  and  its 
meshes  are  filled  in  with  a  soft  substance  called  spleen- 
ptdp. 

The  pulp  consists  largely  of  red  and  white  blood- 
corpuscles. 

The  blood  brought  by  the  splenic  artery  is  poured 
directly  into  the  spleen-pulp  and  comes  directly  in  con- 
tact with  the  cells  and  tissues  there. 

The  spleen  appears  to  be  concerned  in  the  production 
of  white  corpuscles  and  in  the  elimination  of  worn-out 
red  ones. 

The  exact  function  of  the  spleen  is  not  yet  fully 
known. 


142  TIIIED    BOOK    OF   PHYSIOLOGY 

Blood. — Blood  is  a  liquid  which  is  composed  of  all 
the  substances  needed  to  nourish  and  maintain  the  life 
of  the  cells.  It  constitutes  about  one-thirteenth  of  the 
weight  of  the  body. 

Blood  has  three  great  duties  to  perform  :  (1)  to  carry 
to  the  cells  of  the  body  the  food  which  is  taken  up  from 
the  alimentary  canal ;  (2)  to  take  oxygen  from  the  air 
which  we  breathe  and  distribute  it  to  the  cells ;  (3)  to 
gather  up  waste  matter,  such  as  carbon  dioxide,  water, 
and  urea,  and  carry  them  to  the  excretory  organs,  where 
they  are  cast  out. 

Blood  is  composed  of  blood-plasma,  red,  corpuscles,  and 
white  corpuscles. 

Blood-plasma. — Blood-plasma  is  the  purely  liquid 
pait  of  the  blood.  About  90  per  cent,  of  it  is  water. 
In  solution  in  the  water  are  the  proteids,  which  consti- 
tute about  8  or  9  per  cent,  of  the  plasma,  and  the  carbo- 
hydrates, fats,  and  minerals,  which  form  about  2  per 
cent. 

In  addition  to  these  is  a  small  quantity  of  another 
substance  called  fibrinogen,  which  causes  blood  to  clot. 

Red  corpuscles. — After  blood  has  passed  through 
the  capillaries  of  the  lungs  it  has  a  bright  red  coloi-. 
The  only  part  of  the  blood  having  this  color,  however, 
is  the  red  corj)uscle. 

Red  corpuscles  are  very  small,  circular  discs,  whicli 
are  concave  on  both  sides.  They  are  about  saVo  i'^^'l^  ^^ 
diameter  and  one-fourth  as  thick.     It  has  been  calcu- 


CIKCULATIO.N 


14:5 


lated  that  tliere  are  5,000,000  of  Uhmh  in  a  drop  of  blood 
as  larj;:e  lus  a  ])inhrad.     When  only  a  lew  are  s(M'n  lliey 
are  faintly  red,  but  a  great  number 
tojjether  give  a  deep- red  coh)r. 

Fig.  71  shows  the  appearance  of 
human  bhxxl  when  it  is  spread  ex- 
ceedingly thin  under  a  compound 
microscope. 


Hemoglobin.  —  The    function        Fig.    to— Red   eor- 
of  the   red   corpuscle   is   to   carry      P"^^^^^-   «,  «,  ;^  ""'nber 

joined  ;   6,  6,  side  view  ; 

oxygen  out  from  the  lungs  to  the      ^^  ^iew  of  edi^e. 
tissues  of  the  body.     It  is  made  up 

of  a  fine,  spongy  framework  called   the  stroma,   in  the 
meshes  of  which  is  a  substance  called  hemoglobin. 


Fig.  71. — lilnod  .-i.-t-u  uudfi  a  luicrctsuupe. 


This  substance  is  the  most  important  part  of  the  cor- 
puscle. It  is  a  proteid  substance  and  contains  iron.  Its 
great  value  lies  in  the  fact  that  it  will  readily  combine 
with   oxygen   \n   the  lungs,   and   then,   floating    in   the 


144  THIET)    BOOK    OF    PHYSIOLOGY 

plasma,  will  carry  the  oxygen  uiit  to  the  tissues  aud  give 
it  up  to  them. 

The  hemoglobin  is  red  when  it  is  oxidized,  but  as  soon 
as  it  loses  the  oxygen  it  turns  purple.  Hence  the  differ- 
ence in  the  color  of  blood  before  and  after  passing 
through  the  capillaries  of  tissues. 

Origin  of  red  corpuscles. — Red  corpuscles  per- 
form their  part  for  a  certain  length  of  time,  and  when 
worn  out  are  brought,  it  is  thought,  to  the  spleen,  where 
they  are  disintegrated.  Xew  ones  must  then  he  set 
adoat  at  some  point  in  the  body.  This  appears  to  be 
done  in  the  red  marrow  of  the  bones,  for  at  that  place 
are  found  colored  cells  with  a  nucleus,  and  from  them 
appear  to  come  the  unnucleated  discs  called  the  red 
corpuscles. 

White  corpuscles. — White  cori^uscles  are  masses 
of  protoplasm  with  one  or  more  nuclei.  They  are  usu- 
ally larger  than  red  corpuscles,  but  are  not  nearly  so 
numerous.  When  at  rest  they  are  sx^herical  in  form,  but 
are  capable  of  assuming  a  great  variety  of  shapes,  very 
much  like  the  amoeba  described  on  page  21. 

White  corpuscles  are  carried  along  by  the  blood,  but 
are  not  confined  by  the  blood-vessels,  for  they  can  jDass 
out  through  the  walls  into  the  tissues  when  necessary. 

Function  of  white  corpuscles.  —  White  cor- 
puscles move  about  in  the  blood  and  through  the  tissues 
of  the  body,  apparently  without  anything  to  do,  but 
alwavs  on  the  lookout  for  somethins:  to  do. 


CiUCULATloX  145 

They  have  l)eeii  called  the  scavengers  of  the  lK)dy,  be- 
cause if  they  meet  any  foreign  substance  they  at  once  set 
a]>out  to  remove  it. 

The  foreign  matter  is  taken  into  their  own  bodies  and 
dissolved  or  carried  out  to  the  surface.  This  is  often 
done  at  the  sacrifice  of  their  own  lives  to  save  the 
body. 

When  tht*  skin  or  mucous  lining  is  cut  or  l^roken, 
germs  of  disease  will  lo^ige  there  and  begin  to  multiply 
and  feed  on  the  tissues.  When  this  happens,  the  white 
corpuscles  collect  about  the  spot  in  great  numljers  and 
attack  the  invading  germs. 

In  such  a  case  the  white  corpuscles  are  like  a  standing 
army  called  upon  to  repel  an  invasion.  If  the  army  is 
strong,  a.s  it  is  in  good  health,  it  usually  comes  off  victo- 
rious. Many  of  the  corpuscles,  however,  must  sacrifice 
themselves  in  the  contiict,  and  the  pus  in  a  wound  i»  a 
mass  of  their  dead  bodies. 

Blood-clots. — While  the  blood  is  in  the  living  body 
it  is  a  thin  liquid.  But  as  soon  as  any  is  allowed  to 
escape  it  becomes  thick,  and  forms  the  blood-clot.  After 
blood  has  stood  for  an  hour  or  more  the  clot  shrinks 
in  size,  and  a  yellow  liquid  called  serum  runs  from  it. 
Serum  is  just  like  plasma,  except  that  the  fibrinogen  is 
wanting.     (See  page  142.) 

The  clotting  is  due  to  the  fibrinogen,  which,  for  some 
cause  unknown,  is  changed  into  a  great  number  of  inter- 
lacing fibres  (fnWedJibrin. 

The  threads   of  fibrin   gradually   contract   and  gather 

10 


146 


THIED   BOOK   OF   PHYSIOLOGY 


up,  as  in  a  net,  all  tlie  corpuscles  and  squeeze  out  the 
serum.     This  operation  is  called  coagulation. 

Fibrin  can  easily  be  separated  if  some  fresh  blood, 
secured  at  the  slaughter-house,  be  whipped  with  a  bun- 
dle of  twigs.  The  fibrin  will  adhere  to  the  twigs,  and 
can  then  be  washed  and  examined. 

The  circuit  of  the  blood. — After  this  study  of  the 
various  organs  of  circulation  and  their  function,  we  are 

ready  to  follow  the  blood 


A 


B 


in  its  circuit  through  the 
body. 

Since  only  pure  blood 
is  ready  for  distribution, 
and  the  left  ventricle  of 
the  heart  is  the  chief 
agent  in  sending  it  out, 
the  proper  place  to  begin 
the  circuit  is  at  the  left 
ventricle  of  the  heart. 
This  cavity,  as  we  have 
learned,  is  surrounded  by  very  heavy  muscular  walls 
capable  of  hard  work.  When  filled  with  red  blood,  the 
muscle-fibres  shorten,  thus  closing  the  cavity  and  forcing 
the  blood  out  through  the  semilunar  valves  into  the 
aorta.  This  great  artery  communicates  by  numerous 
branches  to  every  tissue  of  the  body. 


Fig.  72. — Section  through  the 
ventricles  of  the  heart.  A^  when 
ventricles  are  filled  with  blood  ;  B^ 
just  after  contraction. 


In  the  arteries. — The  walls  of  the  arteries  are  com- 
posed in  part  of  elastic  tissue.     The  left  ventricle  forces 


CIRCULATION  147 

a  quantity  of  blood  into  them  at  every  beat.  Thus  the 
arteries  are  kept  so  full  that  their  elastic  walls  are 
stretched.  We  can  now  s«*e  the  use  of  the  semilunar 
valves  to  keep  the  blood  in  the  aorta  until  the  left  ven- 
tricle can  fill  up  again.  The  arti^ries  thus  exert  a  steady 
pressure  upon  the  blood  within  them. 

Pulse. — New  blood  is  forced  into  the  aorta,  which  is 
already  full  and  distended.  This  causes  a  wave  or  j;w/«e 
to  pass  over  it.  The  pulse  may  be  felt  at  5iny  point 
where  the  artery  comes  close  to  the  surface.  Blood 
passes  through  the  large  arteries  at  the  rate  of  about  one 
foot  per  second  ;  but  it  is  not  the  rush  of  blood  that  causes 
the  pulse. 

The  fresh  ventricle-full  of  blood  causes  a  sudden  en- 
largement of  the  aorta  at  the  point  where  it  enters,  and 
it  is  this  distention  which  travels  as  a  wave,  or  i^ulse, 
along  the  artery. 

Control  of  quantity  of  blood  in  an  artery. — 

One  of  the  coats  of  the  wall  of  an  artery  is  composed  of 
muscular  fibres  which  pass  around  the  artery.  When 
these  contract  they  make  the  artery  smaller,  and  when 
they  relax  they  j)ermit  the  elastic  tissue  to  stretch,  and 
the  artery  may  become  larger.  In  this  way  the  quantity 
of  blood  which  may  flow  to  any  part  of  the  body  can  be 
regulated. 

The  action  of  these  muscles  is  under  the  control  of  the 
sympathetic  nervous  system,  as  will  be  explained  later. 

The  flow  of  blood  is  not  under  control  of  the  will,  but 


148  THIED   BOOK    OF   PHYSIOLOGY 


Fig.  73. — Scheme  showing  the  circulation  of  the  hlood.  RA^  right 
auricle;  BV,  right  ventricle;  PA,  pulmonary  artery;  L,  capillaries 
of  lungs  ;  PV,  pulmonary  vein  ;  LA,  left  auricle  ;  LV,  left  ventricle  ; 
AO,  aorta;  Sc,  Sc,  subclavian  arteries;  c,c,  carotid  arteries;  A,  A, 
capillaries  of  arms  ;  77,  capillaries  of  head  ;  CA,  coeliac  artery  ;  HA, 
hepatic  artery  ;  SA,  splenic  artery  ;  GA,  gastric  artery  ;  G,  capillaries 
of  stomach  ;  Sp,  capillaries  of  spleen  ;  PV,  portal  vein  ;  Li,  capil- 
laries of  liver;  HV,  hepatic  vein;  MA,  mesenteric  artery;  I,  capil- 
laries of  intestines  ;  MV,  mesenteric  vein  ;  RA,  renal  artery  ;  K,  1, 
capillaries  of  Malpighian  bodies  of  the  kidneys  ;  K,  2,  capillaries  about 
the  tubules  of  kidneys  ;  RV,  renal  vein  ;  LE,  capillaries  of  lower  ex- 
tremities ;  A  VC\  ascending  vena  cava ;  D  VC,  descending  vena  cava. 


ClJiCULATlOI^ 


149 


150  THIRD   BOOK   OF   PHYSIOLOGY 

certain  kinds  of  emotion  may  result  in  such  a  contraction 
of  the  arteries  carrying  blood  to  the  head  that  the  face 
may  become  very  pale,  and  fainting  may  result  from  lack 
of  blood. 

Other  kinds  of  emotion  may  cause  the  muscles  to  relax 
and  a  large  quantity  of  blood  will  come  to  the  face, 
causing  blushing. 

Exposure  to  cold  will  cause  the  arteries  near  the  sur- 
face to  contract,  and  so  the  skin  becomes  white.    Warmth 
will  relax  them,  and  a  ruddy  color  comes  with   an   in 
creased  supply  of  blood. 

Blood  in  the  capillaries.— The  arteries  have  di- 
vided into  countless  small  branches,  and  the  blood  in  a 
steady  stream,  and  without  any  pulse,  now  leaves  them 
and  enters  the  capillaries.  Here  the  exchange  takes  place 
between  the  blood  and  the  tissues.  The  nature  of  the 
exchange  will  depend  on  the  contents  of  the  blood  and 
the  nature  of  the  tissue  through  which  the  capillaries 
pass.  In  the  liver  one  kind  of  exchange  will  occur  ;  in 
the  kidneys,  another  kind  ;  in  the  villi,  the  lungs,  the 
muscle,  the  bone,  and  the  skin,  still  other  kinds.  In  all 
cases,  however,  the  exchange  occurs  through  the  walls 
of  capillaries. 

Systems  of  circulation. — There  is  but  one  great 
system  of  circulation,  for  the  blood  which  leaves  the  left 
ventricle  of  the  heart  will  return  to  the  same  point  again. 

For  convenience,  however,  the  circuit  may  be  divided 
into    several    systems    depending    on    certain    marked 


CIIM'IU.ATTON  151 

changers  effected   in   llic   blood   at  various  points  in  its 
ciiTuit. 

The  most  important  divisions  are  tlie  systeviic,  the 
poriol,  the  renal,  and  the  pulmonary. 

Systemic  circulation. — Blood  is  supplied  by  the 
arteries  to  the  cells  of  every  tissue  of  the  body.  This  is 
the  general  or  si/stemic  circulation.  By  this  system  blood 
is  carried  to  the  capillaries  about  the  cells  of  muscle, 
bone,  nerve,  and  all  other  tissues.  In  these  capillaries 
the  blood  loses  the  materials  needed  for  the  repair  and 
growth  of  the  cell,  and  for  energy.  These  pavSs  by  os- 
mosis into  the  lymph  about  the  cell.  At  the  same  time 
the  blood  gains,  by  osmosis  into  the  capillaries,  carbon 
dioxide,  water,  and  urea. 

Distinction  must  be  made  between  the  systemic  circu- 
lation, where  blood  is  supplied  for  the  benefit  of  the  cells, 
and  the  other  kinds  of  circulation,  where  blood  is  forced 
through  capillaries  of  various  organs  that  it  may  be 
modified  or  purified.  All  these  latter  changes  are  for 
the  benefit  of  the  systemic  circulation. 

The  portal  circulation. — The  blood  which  is 
furnished  by  the  systemic  circulation  to  the  stomach, 
intestines,  pancreas,  and  spleen  supplies  the  needs  of 
the  cells  of  those  organs,  and  also  furnishes  materials 
needed  for  the  juices  used  in  digestion.  In  exchange  for 
these,  the  blood  takes  up  a  supply  of  food  which  has 
passed  from  the  digestive  tract  into  the  capillaries  of  the 
stomach  and  intestines. 


152  THIED   BOOK   OF   PHYSIOLOGY 

The  blood  is  now  gathered  up  from  these  four  organs 
by  minute  veins  which  unite  into  one  large  one  called 
the  portal  vein.  Through  it  this  blood  is  conducted  to 
the  liver,  where  it  passes  through  a  second  set  of  capil- 
laries and  is  changed  1u  a  manner  explained  on  page  129. 

This  is  the  only  place  in  the  body  where  a  vein  sup- 
plies blood  to  capillaries. 

Renal  circulation. — Two  branches  of  the  ab- 
dominal aorta  carry  blood  to  the  kidneys.  Some  small 
branches  of  these  are  made  to  supply  blood  to  the  tissues 
of  the  kidneys,  but  most  of  the  blood  passes  through 
another  system  of  bodies,  to  be  described  later.  The 
blood  here  loses  a  great  deal  of  water  and  urea.  Just 
after  the  blood  passes  through  the  kidneys  it  is  probably 
purer  than  at  any  other  point  in  its  circuit. 

In  the  veins. — After  any  portion  of  blood  has 
fulfilled  its  purpose  in  circulation,  it  is  gathered  up  and 
brought  back  to  the  heart  by  the  regular  system  of  veins. 
The  color  of  the  blood  is  now  a  purple,  because  that  is 
the  color  of  hemoglobin  when  it  loses  its  oxygen. 

Pulmonary    circulation. — Although   the   blood 

has  returned  to  the  heart,  it  is  bj^  no  means  back  to  our 
starting- place  at  the  left  ventricle.  It  has  only  reached 
the  right  heart. 

The  superior  and  inferior  vena  cava  now  pour  the  blood 
into  the  right  auricle,  whence  it  flows  into  the  right  ven- 
tricle.    The  walls  of  the  right  ventricle  now  close  in 


CIRCULATION  153 

upon  it,  slnittiii^^  tlic  Iricnspid  valve  and  forcing  it  out 
into  thvi  puhnonari/  aftcnj  and  on  to  the  lungs. 

When  the  blood  started  out.  from  the  left  ventricle  it 
was  a  bright  red,  showing  that  the  red  corpuscles  were 
loaded  with  oxygen.  When  it  passed  through  the  capil- 
laries of  the  systemic  system  the  oxygen  was  given  up  to 
the  cells  there,  and  the  color  of  the  corpuscles  changed  to 
purple. 

The  pulmonary  artery  is  the  only  artery  that  carries 
purple  blood. 

In  the  lungs  an  important  exchange  is  made.  Blood 
gives  up  carbon  dioxide,  water,  and  certain  organic  im- 
purities to  the  air  in  the  air-sacs,  and  takes  in  return  a 
fresh  supply  of  oxygen. 

The  blood  is  now  a  bright  red  again  and  is  conducted 
by  the  pulmonary  veins  to  the  left  auricle.  Thence  it 
flows  into  the  left  ventricle.  The  circuit  is  now  com- 
plete. 

Heart-beats. — ^The  two  auricles  contract  and  relax 
together.  Likewise  the  two  ventricles.  While  the  ven- 
tricles are  contracting  the  auricles  are  filling,  and  as 
soon  as  the  ventricles  relax  the  auricles  contract. 

As  explained  before,  the  auricles  are  hardly  more 
tlian  small  reservoirs  to  hold  blood  while  the  valves 
below  them  are  closed.     Their  contraction  is  but  feeble. 

The  alternate  contraction  and  relaxation  of  the  ven- 
tricles may  be  felt  at  a  point  where  the  apex  of  the 
heart  is  close  to  the  chest-wall.  This  point  is  to  the  left 
of  the  sternum,  between  the  fifth  and  sixth  ribs. 


154  THIRD   BOOK   OF   PHYSIOLOGY 

Sounds  of  the  heart. — If  the  ear  be  pressed  tightly 
upon  the  point  directly  over  the  apex  of  the  heart,  two 
distinct  sounds  are  heard  during  each  beat.  They  are 
similar  to  the  sounds  made  in  pronouncing  the  syllables 
loob  dup.  The  sounds  are  caused  by  the  action  of  the 
valves.  The  mitral  and  tricuspid  valves  close  at  the 
same  time,  producing  the  sound  loob.  When  the  ven- 
tricles relax,  the  l)ack  pressure  of  the  elastic  aorta  sud- 
denly closes  the  semilunar  valves,  causing  the  sound 
(iTq). 

Work  of  the  heart. — The  heart  of  an  adult  beats 
about  seventy-two  times  every  minute.  The  ventricles 
have  to  force  the  blood  into  the  arteries  against  a  strong 
back  pressure,  and  they  must  continue  to  do  this  about 
sevent^^-two  times  a  minute  during  life. 

As  a  consequence  the  heart  is  the  hardast- worked 
organ  in  the  body.  If  a  strong  man  would  carry  upon 
his  shoulder  a  weight  of  200  i^ounds  to  the  top  of  a 
mountain  2000  feet  high,  he  would  have  done  no  more 
work  upon  the  weight  than  the  heart  does  every  day 
upon  the  blood. 

Rest  and  nourishment  of  the  heart. — After 
each  contraction  of  the  heart  there  is  a  period  of  relaxa- 
tion and  rest  which  is  even  longer  than  the  time  of 
contraction. 

Thus  the  heart  rests  more  than  half  the  time,  though 
each  period  of  rest  is  short. 

The  muscles  of  the  heart  are  well  supplied  with  blood. 


CIRCULATION  155 

The  first  branch  from  the  aorta,  just  above  the  heart,  is 
the  coronary  artcrii,  which  carries  blood  directly  to  the 
imiscles  of  the  heart  and  supplies  the  cells  with  food. 
The  heart  gets  no  nourishment  from  the  blood  while  it  is 
in  the  auricles  and  ventricles. 

Hygiene  of  circulation. — A  x^igorous  circulation 
oi good  blood  is  sure  to  result  in  good  health  and  a  rapid 
recovery  from  temporary  illness  or  accidental  injury. 
But  good  blood  is  possible  only  under  the  four  con- 
ditions already  pointed  out.  (1)  A  plentiful  supply  of 
nourishing  food  must  be  taken  into  the  blood-current 
from  the  alimentary  tract.  (2)  The  blood  must  be  sup- 
plied with  an  abundance  of  oxygen  from  the  air  in  the 
lungs.  (3)  The  kidneys,  liver,  lungs,  and  other  excre- 
tory organs  must  take  from  the  blood  the  waste  products 
and  other  substances  no  longer  of  use  in  the  blood.  (4) 
The  nervous  system  must  be  able  to  control  the  tlow  of 
blood  and  to  direct  it  to  the  point  where  it  is  most 
needed. 

Effect  of  exercise  on  the  circulation. — It  is 
observed  that  exercise  increases  the  rapidity  of  the 
heart-beats.  This  results  in  a  more  rapid  flow  of  blood, 
deeper  breathing,  and,  in  time,  hunger.  Blood  is  sup- 
plied in  larger  quantity  to  any  part  of  the  body  that  is 
active.  An  exercise  that  calls  into  action  every  part  of 
the  body  will  quicken  the  flow  of  blood  through  the  en- 
tire system.  Such  exercise  frequently  repeated  tends  to 
build  up  a  stronger  body. 


156  THIED   BOOK   OF   PHYSIOLOGY 

Contraction  of  the  muscles  and  movements  of  the 
body  also  assist  circulation  in  a  mechanical  way.  The 
veins  and  lymphatics  are  supplied  with  numerous 
valves,  so  that  any  pressure  upon  them  will  always  push 
the  liquid  within  them  towards  the  heart,  for  the  valves 
will  prevent  any  movement  in  the  opposite  direction. 

Since  many  veins  and  lymphatics  lie  near  the  surface, 
any  tight  bands  or  clothing  will  seriously  impede  the  cir- 
culation at  any  time,  but  particularly  during  exercise. 

Colds. — The  cause  of  ^^  colds"  is  not  certainly  known, 
but  they  appear  to  be  closely  connected  in  some  way  with 
the  circulation  of  the  blood. 

An  exposure  to  cold  weather,  to  wet,  or  to  drafts  of 
air  may  contract  the  blood-vessels  on  the  surface  of  the 
body  and  bring  about  a  condition  called  a  cold.  What- 
ever may  be  the  exact  cause,  it  is  known  from  expe- 
rience that  colds  may  be  avoided  by  maintaining  a  vigor- 
ous circulation  by  exercise  and  deep  breathing.  ^Yoolen 
clotliing  assists  in  preventing  sudden  changes  in  surface 
temperature. 

Bleeding  from  a  wound.— Y^^hen  a  vein  is  punc- 
tured, the  blood  oozes  out  in  a  steady  stream  because  it  is 
not  under  pressure.  The  bleeding  may  be  stopped  by  a 
bandage  on  the  side  of  the  wound  farthest  from  the 
heart. 

When  an  artery  is  severed,  the  blood  issues  in  a  stream 
with  considerable  force,  which  increases  with  each  beat 
of  the  heart.     Such  a  wound  needs  immediate  attention. 


riRCULATloN  157 

The  bleeding  may  be  temporarily  checked  by  a  tight 
bandage  on  the  side  of  the  wound  towards  the  heart. 
The  bandage  must  be  tight,  as  the  arteries  usually  lie 
deep  in  the  tlesh. 

Effect  of  alcohol  on  the  heart.— Under  some 
conditions  the  heart  may  beat  faster  after  a  person  takes 
an  alcoholic  drink,  but  such  quickened  action  is  not  due 
to  any  strengthening  action  of  alcohol  on  the  heart  itself, 
as  was  once  supjiosed.  It  is  due  rather  to  distuibance 
of  the  nerves  in  other  parts  of  the  bod}-. 

The  mere  act  of  swallowing  or  sipping  cold  water  will 
increase  the  beating  of  the  heart,  and  so  will  swallowing 
anj'  hot,  biting  substance,  as  pepper  or  ginger  tea,  be- 
cause of  the  sensitiveness  and  complex  relations  of  the 
nervous  system.  AVhen  the  heart  beats  faster  after  taking 
an  alcoholic  drink,  the  result  is  chiefly  due  to  such  dis- 
turbance of  the  nerves,  for  when  care  Ls  taken  to  avoid 
all  irritation  of  the  throat  and  stomach  in  giving  an  alco- 
holic drink,  little  or  no  change  in  the  heart-beat  occurs. 
Muscular  action  also  makes  the  heart  beat  faster,  and  so 
in  all  exact  tests  of  this  kind  the  person  taking  the  alco- 
hol is  kept  quiet  and  away  from  the  company  of  others. 
Under  such  precautions  it  is  seldom  that  any  change  in 
the  heart's  action  occurs,  showing  that  the  old  notion 
that  alcohol  is  a  stimulant  or  a  source  of  strength  for  the 
heart  is  false. 

Instead  of  being  a  benefit  to  the  heart,  alcoholic  drinks 
are  a  fruitful  source  of  heart  disease.  German  physicians 
have  begun  to  observe  that  in  cities  where  the  most  beer 


158  THIRD    BOOK    OF   PHYSIOLOGY 

is  drunk  they  have  the  largest  number  of  cases  of  heart 
disease. 

Alcohol  and  the  arteries. — It  has  been  explained 
that  the  supply  of  blood  through  the  arteries  is  regu- 
lated by  muscles  under  control  of  the  nervous  system. 
A  large  dose  of  alcohol,  such  as  is  contained  in  a  drink 
of  whiskey,  will  disturb  the  controlling  power  of  the 
nervous  system  and  allow  the  arteries  to  relax,  and  warm 
blood  flows  freely  out  to  the  surface  of  the  body. 

Thus  the  heat  can  rapidly  radiate  and  the  tempera- 
ture of  the  whole  body  is  reduced. 

For  this  reason  those  who  drink  alcoholic  liquoi^s  suffer 
more  and  will  be  more  quickly  frozen  from  long  exposui^e 
to  cold. 

Alcohol  and  oxygen. — The  oxygen  forms  only  a 
loose  chemical  combination  with  the  hemoglobin  of  the 
red  corpuscle.  Alcohol  has  a  strong  afl&nity  for  oxygen, 
and.  when  mingled  with  the  blood,  robs  the  corpuscles 
of  the  oxygen  which  should  go  to  the  tissues. 

YThile  the  oxidation  of  the  alcohol  will  produce  heat, 
it  is  at  the  expense  of  the  bodily  health  and  vigor. 

Tobacco  and  the  circulation. — Experience  shows 
that  the  nicotine  of  tobacco  is  injurious  to  the  organs  of 
circulation,  particularly  to  the  heart. 

The  heart-beat  often  becomes  irregular  and  spasmodic. 
It  is  claimed  by  reputable  physicians  that  much  of  the 
heart- trouble  and  heart-failure  is  caused  by  the  use  of 
tobacco. 


CIRCULATION  15!) 

Tobacco  is  particularly  harniful  lo  voulli   uiidri- lliirty 
years  of  a«;e. 

QUESTIONS   FOR    KEVIKW. 

1.  Why  is  circuhition  lu'ct'ssary? 

2.  How  (Iocs  food  get  from  the  stomach  and  iuteHtiiU'H  into  the 
blood  ? 

3.  What  is  tlic  use  of  glycogen? 

4.  Give  three  functions  of  the  liver. 

5.  Name  the  organs  of  circulation. 

6.  What  is  the  heart?     Its  size,  shape,  and  position. 

7.  Describe  the  pericardium. 

8.  Describe  the  cavities  of  the  heart. 

9.  Name  and  locate  the  valves  of  the  heart. 

10.  Make  drawings  to  show  the  manner  of  action  of  the  valves. 

11.  IMake  drawing  and  trace  the  course  of  the  blood  in  the  heart. 

12.  What  are  arteries  ?    Describe  their  coats. 

13.  What  is  the  function  of  the  pulmonary  artery  ? 

14.  Describe  the  course  of  the  aorta. 

15.  What  are  capillaries?    What  does  the  word  mean? 

16.  What  is  the  location  and  size  of  capillaries? 

17.  What  is  the  function  of  the  capillaries? 

18.  How  does  food  get  from  the  capillaries  to  the  cells? 

19.  How  is  the  blood  collected  again  ? 

20.  Describe  the  structure  of  a  vein. 

21.  What  kind  of  valves  in  veins?     How  may  their  location  be 
observed  in  surface  veins? 

22.  What  is  the  function  of  the  lymphatics  ? 

23.  Describe  the  two  large  lymphatic  ducts. 

24.  What  are  "  waxen  kernels"  ? 

25.  What  is  the  construction  of  the   lymphatic  nodes?     What 
their  function? 

26.  Describe  the  spleen. 

27.  How  much  blood  in  a  man  who  weighs  200  ptjunds? 

28.  State  three  important  uses  of  blood. 


160  THIED    BOOK    OF   PHYSIOLOGY 

29.  What  is  the  composition  of  blood  ? 

30.  Describe  blood-plaaraa. 

31.  Give  a  full  account  of  the  red  corpuscles. 

32.  What  is  the  function  of  hemoglobin  ? 

33.  What  is  the  origin  of  the  red  corpuscle  ? 

34.  Describe  the  white  corpuscle.      AVhat  is  its  origin  ? 

35.  Of  what  use  is  the  white  corpuscle? 
35.  What  is  fibrin  ?     How  is  it  formed  ? 

37.  Beginning  at  the  left  ventricle,  trace  the  blood  in  a  complete 
circuit  through  the  body.  (It  will  take  some  time  to  prepare  and 
answer  this  question,  but  it  should  be  done.  The  answer  will  in- 
clude all  matter  from  page  146  to  153,  and  should  be  prepared  by 
each  pupil  for  one  continuous  recitation.) 

38.  Explain  the  beating  of  the  heart. 

39.  Describe  the  sounds  of  the  heart. 

40.  How  much  work  does  the  heart  do? 

41.  What  is  the  coronarv  artery? 

42.  What  four  conditions  will  supply  good  blood? 

43.  How  does  exercise  affect  circulation? 

44.  What  is  the  effect  of  alcohol  on  circulation  ? 

45.  How  does  blood  flow  from  a  cut  in  an  artery?  How  from  a 
vein*?     Why? 

40.     What  should  be  done  when  an  art«ry  is  severed? 
47.  On  which  side  of  an  artery  must  pressure  be  applied  to  stop 
bleeding?     Why?     How  in  case  of  a  vein ?     Why? 

EXPERIMENTS. 
Fibrin. — Secure  a  quart  of  fresh  blood  at  the  slaughter-house.  Take  a 
stock  of  broom  or  a  bundle  of  fine  twigs  and  beat  it  in  the  manner  of  beating 
eggs.  The  fibrin  will  cling  to  the  broom,  and  the  red  corpuscles  adhering  to  it 
can  be  rinsed  off  with  water.  After  the  fibrin  i.>  taken  out,  the  remaining  part 
will  not  coagulate,  however  long  it  may  stand. 

Serum. — Allow  some  fresh  blood  to  stand  for  a  time  in  a  glass  jar.    A  clot 
will  form  in  the  centre,  and  a  yellowish  liquid,  the  serum,  will  .separate  from  it. 


("IKcn.A'noN  h;i 

To  show  the  pulee  at  the  wrist.  -Secure  u  .small  piccr  (if  mirror 
alHuit  V|  inch  s(iiuire,  iiiul  fa.sten  it  with  wax  <»iito  the  point  in  the  wri.st  where 
the  i>ulse  i.s  mo.st  plainly  felt.  Re.st  the  hand  near  a  window  in  such  j>osition 
that  the  sunlight  will  be  reflecte<l  to  the  ceiling  of  the  room.  At  every  beat  of 
the  heart  the  bright  spot  on  the  celling  will  move  back  and  forth  through  a  ff)ot 
or  more. 

To  illustrate  the  principle  of  the  pulse.— Connect  one  end  (..f  a 
heavy  rubber  tube  to  a  water-tap.  Turn  the  water  on,  and  then  close  the  other 
end  of  the  tube  until  water  i.s.sues  in  a  .«<mall  stream  under  pressure.  The  tube 
will  be  stretched  and  rigid  like  a  large  artery.  Now  suddenly  open  and  close  the 
water-faucet,  and  the  i>ulse  aloyg  the  rubber  tube  may  be  felt  each  time  fre-sh 
water  is  admitted. 

Examination  of  the  heart.— Secure  from  the  butcher  an  ox  heart. 
Carefully  examine  the  exterior  and  the  number  of  tubes.  Dissect  and  examine 
the  cavities.    Search  for  the  valve.<;.    Notice  the  thickness  of  the  walls. 

To  examine  red  corpuscles.-Puncture  the  skin  of  the  thumb  with  a 
needle  and  let  out  a  small  drop  of  blood.  Spread  the  blood  on  a  slip  of  glass, 
and  examine  under  a  compound  microscope.  The  blood  must  be  only  a  very 
thin  smear  on  the  glass,  or  the  separate  corpuscles  will  not  be  seen. 


11 


CHAPTER    XI 


RESPIRATION 


The  ocean  of  air. — The  air  is  a  great  ocean  of  gas 
which  forms  the  outer  layer  of  the  earth.  Air  moves  with 
the  earth,  and  is  a  part  of  it.     Nothing  is  outside  the 


Fig.  74. — The  three  envelopes  of  the  earth.     Man's  abode  i=  at  the 
bottom  of  the  outer  haver. 


earth  unless  it  is  beyond  this  layer  of  air.  Man,  properly 
speaking,  lives  beneath  the  surface  of  the  earth.  His 
natural  place  is  in  the  plane  where  the  ocean  of  air  rests 
upon  the  oceans  of  water  and  the  land. 

162 


RRSPI  RATION  163 

Tlie  deptli  of  tlw  mimmhI  ocean  is  not  known,  for  it  luis 
no  definite  snrface  at  tlie  top,  but  shades  off  into  lighter 
and  ligliter  air  until  none  exists.  It  is  very  probable 
that  some  air  exists  as  hi«j:h  as  1000  miles  al)ove  the  lands 
and  watei*. 

Since  air  has  weight,  tin;  layer  next  to  the  land  is 
pressed  upon  with  considerable  force.  At  sea  level  tlie 
pressure  is  about  14.7  jKninds  on  every  square  inch  of 
surface.  Since  air,  like  all  gases,  is  very  compressible,  it 
is  quite  dense  at  the  bottom.  Each  cubic  foot  of  air  at 
sea  level  will  weigh  1.28  ounces. 

Man  and  other  land  animals  are  fitted  to  live  in  this 
lower  dense  layer  of  air. 

The  air  is  composed  of  several  gases  which  are  mixed 
together  by  diffusion. 

The  most  important  one  is  oxygen.  Oxj^gen  is  the 
breath  of  life,  and  man  is  dependent  upon  it  for  every 
minute  of  his  existence. 

The  relation  of  man  to  this  medium  in  which  he  must 
live,  forms  the  topic  of  discussion  in  this  chapter. 

What  respiration  is. — Eespi ration  is  a  process  by 
which  an  exchange  of  gases  takes  place  between  the  air 
and  the  tissues  of  the  body.  The  oxygen,  taken  from  the 
air  in  the  lungs,  is  carried  by  the  red  corpuscles  to  the 
cells  of  the  bod}'.  The  blood  takes  up  in  exchange  the 
carbon  dioxide  and  other  tissue  waste,  and  convej^s  them 
back  to  the  lungs,  where  they  are  given  out  to  the  air. 

This  broad  definition  would  necessitate  oui'  tracing  the 
air  from  the  nostrils  to  the  cells  of  the  body  and  back  again. 


164  THIRD    BOOK    OF    PHYSIOLOGY 

The  part  of  the  process  from  the  lungs  to  the  cells  is 
called  internal  respiration,  and  is  tieated  here  under  the 
subject  of  the  circulation  of  the  blood. 

The  first  part  of  the  process — from  the  nostrils  to  the 
lungs  and  return — is  called  external  respiration,  and  is  the 
proper  subject  of  this  chapter. 

Why  respiration  is  necessary.— Many  very 
small  animals  have  no  lungs  and  no  blood,  and  yet  their 
life,  like  that  (»f  man,  depends  on  their  taking  food  and 
having  it  combine  with  oxygen  of  the  air.  They  are  so 
small,  however,  that  they  do  not  need  special  organs. 
They  absorb  their  food  and  air  through  the  surface  of 
their  bodies. 

In  man  and  all  higher  animals  the  body  is  large,  and 
most  of  the  cells  lie  far  beneath  the  surface.  For  this 
reason  man  needs  special  apparatus  to  carrj^  both  the 
food  and  the  oxygen  to  the  cells. 

What  oxygen  does  for  the  ceUs. — Roughly 
speaking,  it  may  be  said  that  oxygen  does  for  the  body 
what  a  draft  of  air  does  for  the  steam-engine. 

In  the  boiler  of  the  engine  the  oxygen  combines  with 
the  burning  coal,  producing  heat  and  energy,  while 
carbon  dioxide  and  water  pass  up  the  chimney  as  waste 
products  of  combustion. 

In  the  body  the  oxygen  combines  with  the  food  in  the 
cell,  producing  heat  and  energy,  while  carbon  dioxide 
and  water  pass  out  at  the  lungs  as  waste  products  of 
combustion. 


RESPIRATION  1(;5 

Th<'  cell  a|)p«':iis  to  liave  tlie  ability  to  ston*  uj)  hotli 
food  aiul  oxygen  to  a  limited  extent,  and  tln-n  have 
them  unite  in  combustion  when  eni^-oy  and  lieat  are 
needed.  Practically  all  such  combustion  takes  place  hi 
the  cells  and  under  the  control  of  tlie  nervous  system. 

Organs  concerned  in  external  respiration. — 

The  respiratory  tract,  through  which  air  is  brought  into 
close  contact  with  the  blood  in  the  luugs,  consists  of  the 
nostrils,  i)liarijnx^  Jaryrix,  trachea,  bronchi,  bronchial  tabes, 
infundihula,  and  air-sacs.  The  i^assage  of  air  in  and  out 
through  this  tract  is  brought  about  chiefly  by  movement 
of  the  rihs  and  diaphragm. 

The  nostrils. — -The  nostrils  are  lined  with  a  mucous 
membrane,  which  is  always  kept  moist  with  a  secretion 
of  uiucus. 

Particles  of  dust  and  minute  germs  are  lodged  on  the 
sticky  mucus,  and  thus  the  air  is  strained  on  its  entrance 
to  the  respiratory  tract.  The  mucous  lining  is  under- 
laid with  a  net-work  of  blood-vessels,  and  by  this  means 
the  air  is  also  warmed  in  the  nostrils. 

Larynx. — From  the  nostrils  the  air  passes  into  the 
pharynx,  wliicli  has  already  been  described  as  a  box 
with  seven  openings. 

One  of  these  openings  is  the  voice-box,  at  the  top  of 
the  windpipe.     It  is  called  the  larynx. 

Across  the  top  of  the  larynx  are  stretched  the  mem- 
branes called  the  vocal  cords.  The  opening  between  the 
vocal  cords  is  the  glottis.     The  epiglottis  stands  ready  to 


166 


THIRD    BOOK    OF   PHYSIOLOGY 


close  the  glottis  whenever  anything  is  swallowed,  but  at 
all  other  times  the  glottis  is  open.     The  larynx  is  con- 


FiG.  75.— The  larynx.      E,  epiglottis;  A,    "  Adam's  apple. " 

A 

B 


Fig.  TG. — Vocal  cords.  V  F,  true  vocal  cords  ;  P  F,  false  vocal 
cords;  L,  epiglottis.  A^  cords  open,  as  in  breathing  ;  B,  cords  drawn 
close  together,  as  in  speaking  and  singing. 

structed  of  cartilage.     '^Adam's  apple"  is  a  projection 
of  one  of  the  cartilages  of  the  larynx. 


RESPIRATION 


167 


The  trachea. — The  trachea,  or  windpipe,  is  a  tube 
about  one  inch  in  diameter  and  extendin^^  from  tlie 
larynx  downward  for  a  distance  of  al)out  four  and  one- 
half  inches,  when'  it  divides  into  two  l)ranches  called 
the  bronchi. 


Fig.  77. — Tracheu  and  bronchi  showing  the  rings  of  cartilage.     T  to  T, 
trachea  ;  LB,  left  bronchus  ;   RB,  right  bronchus. 


The  trachea  is  kept  open  by  some  sixteen  to  twenty 
incomplete  rings  of  cartilage  of  about  the  shape  of  a 
horse-shoe.  The  incomplete  part  of  the  rings  is  on  the 
posterior  side,  where  the  tube  is  completed  bj^  a  connec- 


168 


THIED   BOOK   OF   PHYSIOLOGY 


tive  tissue.  Against  this  part  lies  the  oesophagus. 
While  food  is  being  swallowed,  the  windpipe  is  more 
or  less  closed  by  the  pressure  upon  its  soft  side. 

The  whole  tube  is  lined  with  mucous  mem])rane  whose 
surface-cells  are  ciliated  epithelium,  (See  page  25.) 
The  cilia  are  an  interesting  example  of  provisions  within 
the  body  for  the  care  and  protection  of  important  or- 
gans.    Cilia  line  nearly  the  whole  respiratory  tract,  be- 


FiG.  78. — Tiifundilmla  and  air-sacs. 


ginning  in  the  nostrils.  Xone  are  found  in  the  air-sacs. 
They  are  not  hairs,  but  minute  projections  of  the  cell 
material  which  wave  constantly  back  and  forth.  Their 
movement  is  more  rapid  in  a  direction  towards  the  outlet 
of  the  air-passages,  and  thus  any  objectionable  sub- 
stance in  the  lungs  or  windpipe  is  slowly  pushed  up  to 
the  throat,  where  it  may  be  coughed  up. 

The  bronchi  have  a  structure  similar  to  that  of  th^ 


RKSIM  RATION 


169 


windpipe,  and  in  fact  are   onlj-  a  continuation  of  the 
windpipe  in  two  branches. 

The  right  bronchus  is  about  one  inch  long,  and  the 
left  one  twice  as  long,  but  of  smaller  diameter. 

Bronchial  tubes.  —  At'ier  the  bronchi  enter  the 
lungs  they  are  called  bronchial  tubes.  These  tubes  divide 
into  smaller  and  smaller  branches,  and  are  distributed  to 
every  part  of  the  lung  tissue.  They  finally  end  in  coni- 
cal expansions  called  infundibula,  which  are  covered  with 


Fig.  79.— The  lungs. 

clustei"S   of   air-sac6    having    somewhat   the   appearance 
shown  in  Fig.  78. 

The  lungs. — The  lungs  are  the  most  important  or- 
gan of  respiration.  They  are  two  in  number,  the  right 
and  left,  and  they  occupy  most  of  the  space  within  the 
walls  of  the  thorax.  The  weight  of  the  two  lungs  to- 
gether is  about  forty  to  fifty  ounces,  the  right  one  being 
somewhat  heavier  and  larger  thau  the  left  one. 


170 


THIRD   BOOK   OF   PHYSIOLOGY 


Lung  tissue  is  composed  of  the  numerous  bronchial 
tubes  with  their  terminal  air-sacs  ;  a  net- work  of  ar- 
teries, capillaries,  veins,  and  lymphatics ;  and  an  abun- 
dance of  elastic  tissue  binding  all  together.  It  is  the 
least  dense  of  all  the  tissues  of  the  body,  being  only 
about  one-half  as  heavy  as  the  same  volume  of  water. 

The   walls  of  the   air-sacs   are  very  thin,   and  blood 


Fig.  80. — Diagram  showing  pleura.  i2,  right  lung;  X,  left  lung; 
e,  entrance  of  bronchi  and  blood-vessels ;  i,  part  of  pleura  which  ad- 
heres closely  to  surface  of  the  lung ;  o,  part  of  pleura  which  adheres 
to  chest' wall.  The  space  between  i  and  o  is  called  the  pleural  cavity, 
though  the  two  are  in  contact ;  D,  diaphragm. 

capillaries  lie  just  outside.  The  sacs  are  very  small,  but 
exceedingly  numerous.  The  total  number  has  been  esti- 
mated at  between  five  and  six  millions,  and  their  total 
area  as  twenty  square  feet.  When  thej^  are  filled  with 
air  the  exchange  of  gases  readily  occurs. 

The  pleura. — Each  lung  is  enclosed  in  a  serous 
membrane  called  the  pleura.  The  pleura  adheres  tightly 
to  the  lung,  and  completely  covers  it  except  at  the  point 


RESPIF^\TION  171 

where  the  bronchi  and  blfKul  tnbes  ont^r  it.  At  this 
point  the  pleura  turns  back,  iis  shown  in  t lie  diagram, 
and  lines  the  walls  of  the  thonix.  Thus  each  pleura  is 
a  closed  sac,  and  there  is  no  communication  from  the 
one  to  the  other. 

The  space  between  the  pleura  on  the  lungs  and  that 
on  the  walls  of  the  thorax  is  called  the  pleural  cavity.  In 
fact,  however,  there  is  no  space  between,  but  the  two 
linings  press  against  each  other.  Since  they  are  very 
smooth  and  are  kej^t  moist  by  secretions,  they  glide  uj^on 
each  other  without  friction  when  the  lungs  move  as  in 
breathing. 

Inhalation. ^ — It  is  a  principle  of  physics  that  a  body, 
free  to  move,  will  always  move  In  the  direction  of  the 
greater  force.  Air  is  no  exception  to  this  law.  If  we  can 
produce  a  condition  in  the  lungs  such  that  the  pressure 
of  the  air  out  through  the  windpipe  is  less  than  the  pres- 
sure inward,  air  will  be  forced  into  the  lungs.  This  con- 
dition is  brought  about  chiefly  ])y  movements  of  the  ribs 
and  diaphragm. 

Action  of  the  ribs. — The  ribs  form  a  true  joint 
with  the  dorsal  vertebrae  and  pass  around  the  chest  to 
the  front,  where  they  (all  but  the  two  pairs  of  floating 
ones)  are  joined  by  their  cartilaginous  ends  to  the 
sternum.  Eibs  do  not  pass  straight  around  the  chest, 
but  droop  considerably  in  front.  The  contraction  of 
muscles  will  raise  the  sternum  and  elevate  the  front  end 
of  the  ribs.     This  will  increase  the  capacity  of  the  chest, 


172 


THIRD   BOOK    OF   PHYSrOLOGY 


and  air  will  rusli  into  the  elastic  lungs  and  expand  them 

till  they  fill  the  chest  as  before. 

The  ribs  also  droop  at  each  side 
of  the  chest,  and  between  them  are 
intercostal  muscles,  which  by  con- 
traction elevate  the  ribs,  and  in  this 
way  also  the  chest  is  enlarged.  (See 
experiment  at  end  of  the  chapter.) 
This  may  be  illustrated  by  the  de- 
vice shown  in  Fig.  81.  The  board, 
B,  represents  the  backbone  5  the 
rings,  E,  the  ribs :  and  the  cylinder, 
the  lungs. 

In  the  first  position  the  rings  just 
permit  the  cylinder  to  pass  through 
them.  In  the  second  position,  where 
the  rings  are  elevated,  there  is  room 
for  a  larger  cylinder  or  for  this  one 
to  expand,  as  the  lungs  would  do. 


Action  of  the  diaphragm. — 

The  diaphragm  has  already  been 
described  as  the  dome-shaped  par- 
tition between  the  thorax  and  the 
abdomen.  The  top  of  the  dome  is 
formed  of  tough  connective  tissue, 

the  enlargement  of  tli-.  ^^^^  which  layers  of  musclc  radi- 
chest  bv  elevation  of  the 

j.-^g     ^  ate   to    the    sides  of   the    thorax. 

When  these  muscles  contract,  the 
diaphragm  is  flattened.     Thus  the  contents  of  the  abdo- 


^Mm 


Fig.    81. — Illuatratini 


RESPMJATION 


173 


men  are  jmslied  down  and  the  chest  is  enlarged,  in  the 
diagram.  Fig.  82,  if  A.  and  B  represent  tlif  chest  and 
abdomen  respectively,  it  is  plain 
that,  if  the  <liaphragni  between 
them  be  flattened,  the  cavity  A  will 
be  enlarged  and  B  will  be  decreased. 
The  air  is  not  drawn  in.  The  en- 
largement of  the  chest  i)roduces  a 
partial  vacuum  there,  and  air  is 
pushed  in  by  atmospheric  pressure. 
As  soon  as  the  density  of  the  air 
within  is  equal  to  that  without,  the 

flow  of  air  will  cease.  ^         ^      ^. 

Fig.    82.  —  Diagram 

illustrating    action    of 
Exhalation. — Any  increase  of      the  diaphragm. 
pressure  within  the  lungs  will  tend 

to  cau.se  an  outward  flow  of  air  called  exhalation.  Ordi- 
nary exhalation  is  accomplished  without  any  muscular 
effort.  The  elastic  tissue  of  the  lungs  alone  tends  to  expel 
the  air,  and  when  the  ribs,  diaphragm,  and  abdominal 
organs  settle  back  to  their  natural  position,  the  capacity 
of  the  chest  is  diminished. 

For  forced  exhalations,  as  in  loud  speaking  and  singing, 
coughing,  and  sneezing,  other  muscles  are  called  into  play. 
Strong  abdominal  muscles  force  the  liver  and  stomach  up 
against  the  diaphragm,  thus  decreasing  the  chest  and 
driving  the  air  out  of  the  lungs.  Also  a  set  of  intercostal 
muscles  upon  contraction  lower  the  ribs,  as  explained  in 
the  experiment  at  the  end  of  this  chapter,  and  in  that 
way  also  the  chest  is  made  smaller. 


174  THIRD   BOOK    OF    PHYSIOLOGY 

Capacity  of  lungs. — Lungs  of  average  size  will  hold 
about  330  cubic  inches  of  air.  In  ordinary  quiet  breath- 
ing only  about  30  cubic  inches  are  inhaled  at  each  in- 
spiration. Thus  only  about  one- tenth  of  the  available  air- 
space of  the  lungs  is  ordinarily  used.  By  an  effort  one 
may  breathe  in  130  cubic  inches  of  air,  and  then  breathe 
out  230  cubic  inches.  About  100  cubic  inches  of  air 
always  remains  in  the  lungs. 

Quantity  of  air  breathed. — The  quantity  of  air 
breathed  varies  greatly  at  different  i^eriods  of  life,  and  in 
various  states  of  the  body  as  to  health  and  exercise.  The 
adult  will,  on  an  average,  breathe  about  eighteen  times 
every  minute.  Thus  he  would  inhale  32,400  cubic  inches 
of  air  every  hour. 

^Vben  at  vigorous  work  or  exercise  he  will  inhale  more 
than  twice  that  amount,  for  his  food  must  be  rapidly  oxi- 
dized to  produce  the  necessary  amount  of  energy.  The 
weight  of  the  air  which  a  man  breathes  is  seven  or  eight 
times  that  of  the  food  eaten. 

Composition  of  air. — AVater  is  composed  of  hydro- 
gen and  oxygen  in  the  proportion  of  two  to  one  i^arts  by 
volume. 

This  is  always  so,  because  water  is  a  chemical  com- 
pound. 

Air,  however,  is  only  a  mixture  of  several  gases,  each 
gas  being  free. 

The  composition,  therefore,  may  vary,  but  the  quantity 
of  the  essential  gases  is  quite  constant. 

Outdoor  air  contains  nitrogen,   oxygen,  water  vapor, 


RESPIRATION  175 

argon,  carbon  dioxide,  ozone,  traces  of  otlMT  g;us<'s,  i)arti- 
cles  of  dust,  and  living  germs. 

Air  i)roper  is  composed  of  five  gas(^s  in  ahoul   tli<;  ])i()- 
portion  named  below. 

PER   CENT. 

Oxygen 20.1H) 

Nitrogen 78.()() 

Argon \.m 

Carbon  dioxide 0.'j 

Ozone 01 

Oxygen  and  ozone. — Oxygen  is  the  i^art  of  the  air 
upon  which  we  are  most  dependent.     It  is  exceedingly 


Fig.  83. — Photograph  of  the  combustion  of  an  iron  wire  in  a  spoon. 
The  spoon  can  he  dimly  seen.  Below  it  U  the  flame  of  a  Bunsen 
burner.     The  white  lines  show  the  paths  of  particles  of  burning  iron. 


active  in  entering  into  chemical  combinations  with  other 
substances.     Its  activity  may  be  shown  in  the  manner 


176  THIRD    BOOK    OF   PHYSIOLOGY 

represented  in  Fig.  83  (see  experiment  iit  end  of  chap- 
ter), where  it  is  rapidly  forming  a  chemical  combination 
with  the  material  in  an  iron  wire. 

Ozone  is  a  concentrated  kind  of  oxygen,  and,  though  it 
forms  but  a  small  per  cent,  of  the  air,  it  plays  an  imj^or- 
tant  part  in  keeping  the  air  pure. 

Nitrogen  and  argon. — Xitrogen  and  argon  are  very 
inert  gases.  Until  recently  they  were  considered  as  one 
gas.  Both  are  important  substances  and  are  necessary 
to  life,  but  they  are  only  passive  agents  in  respiration. 
Oxygen  cannot  be  breathed  in  a  pure  state,  but  must  be 
diluted  with  about  four  times  its  weight  of  nitrogen  and 
argon. 

Carbon  dioxide. — Carbon  dioxide  exists  in  the  air 
in  only  small  quantities,  and  yet  it  is  essential  to  the  life 
of  plants  and,  indirectly,  to  the  life  of  all  animals.  It  is 
one  of  the  essential  foods  of  the  vegetable  world. 

Every  green  leaf,  while  the  sun  is  shining  upon  it,  is 
busy  making  starch  by  a  chemical  union  of  water  and 
carbon  dioxide.  The  leaf  gets  the  water  from  the  sap, 
and  the  carbon  dioxide  from  the  air.  For  every  mole- 
cule of  starch  thus  made,  twelve  atoms  of  oxygen  are  set 
free  into  the  air. 

The  chief  sources  of  carbon  dioxide  are  the  breathing 
of  animals  and  the  burning  of  fuel. 

An  adult  at  work  will  breathe  out  one  cubic  foot  of 
carbon  dioxide  e^'er3'  hour. 

The  burning  of  a  ton  of  coal  will  give  off  about  67,200 
cubic  feet  of  carbon  dioxide. 


RESPIKATION 


177 


For  tivery  100  cubic  feet  of  fuel  gas  consumed,  200 
cubic  feet  of  caibon  dioxide  are  given  to  the  air. 

This  gas  is  constantly  being  used  up  by  the  growing 
vegetation,  and  a  large  (quantity  of  oxygen  is  set  free. 

Thus  vegetables  and  animals  arc  dependent  on  each 
other. 

Changes  iu  inspired  air. — The  blood  which  is  sent 
by  the  right  ^'('nt^icle  of  the  heart  to  the  lungs  is  purple 
because  the  oxygen  has  been  given  up  to  the  tissues.     It 


Fig.  84. — Showing  changes  in  a  green  leaf,     c,   carbon  dioxide  ; 
o,  oxygen;   A,  water  when  in  excess. 


is  also    loaded  with  carbon  dioxide  in   solution  iu  the 
blood-plasma. 

The  two  chief  objects,  then,  in  bringing  the  blood  and 
air  close  together  in  the  lungs  is  that  the  blood  may  get 
oxygen  from  the  air  and  give  out  carbon  dioxide  to  the  air. 

This  exchange  is  made  by  osmosis  through  the  thin 
walls  of  the  air-sacs  and  capillaries. 

The  raj^idity  with  which  gases  will  diffuse  may  be 
shown  by  holding  a  jar  containing  hydrogen  over  a 
porous  cup  containing  air. 

12 


178 


THIED    BOOK    OF   PHYSIOLOGY 


k\^ 


i  eap/7/ 


Fig.  85. — Diagram  illustrating  the  exchange  of  oxygen  and  carbon 
dioxide  between  the  blood  and  air  in  lungs.  0,  oxygen  ;  CO2,  carbon 
dioxide. 


Fig.  86. — Ditfusinn  through  porous  cup.      (See  description  of  experi- 
ment at  end  of  chapter. ) 


RESPIKATION  179 

Till*  hyilioo^en  will  piiss  tli rough  the  walls  of  the  cup 
much  faster  than  the  air  passes  in  the  opposite  direction, 
as  will  be  shown  by  the  escape  of  bubbles  from  the  lower 
end  of  the  tube.  (See  experiments  at  the  end  of  this 
chapter.) 

The  expired  air  is  composed  of  about  15  per  cent,  of 
oxygen,  about  4  per  cent,  of  carbon  dioxide,  78  per  cent, 
of  nitrogen,  and  1  per  cent,  of  argon.  Thus  a  large 
quantity  of  oxygen  is*  taken  from  the  air  and  carbon 
dioxide  added  to  it,  but  other  gases  of  the  inspired  air 
are  not  sensiblj'  changed. 

Hygiene  of  respiration.— Breathing  and  eating 
are  the  two  most  important  things  we  do,  as  far  as  con- 
cerns health  and  vigor  of  both  body  and  mind. 

Just  as  neither  coal  nor  oxygen  would  be  of  any  use  as 
a  source  of  energy  unless  they  could  combine  with  each 
other,  so  also  our  food  and  the  oxygen  must  unite  in  slow 
combustion  within  the  body. 

Just  as  it  requires  good  fuel  and  a  good  draft  of  air  to 
maintain  a  hot  fire,  so  it  takes  good  food  and  good  air  to 
furnish  the  heat  and  energy  needed  in  a  vigorous  body. 

How  air  becomes  impure. — Pure  air  and  proper 
breathing  are  quite  as  essential  as  good  food.  Air  in  the 
open  country  is  pure  because  any  impurities  there  will 
be  mingled  bj'  winds  and  air-currents  with  a  great  mass 
of  air. 

Air  in  the  streets  of  a  crowded  city  is  not  so  pure 
as  in  the  country. 


180  THIRD    BOOK    OF   PHYSIOLOGY 

The  most  impure  air  is  usually  found  in  rooms,  shops, 
railway-carriages,  and  other  enclosures  where  people 
live. 

The  air  in  a  close  room  may  soon  become  unfit  to 
breathe.  Every  respiration  takes  oxygen  from  it  and 
adds  carbon  dioxide  to  it.  A  burning  lamp  is  doing  the 
same.  An  oil-stove,  however  ^'odorless,"  is  vitiating 
the  air  in  the  same  way. 

In  addition  to  the  carbon  dioxide,  certain  poisonous 
organic  substances  are  exhaled  with  each  breath. 

When  such  air  is  breathed  over  again,  the  amount  of 
carbon  dioxide  excreted  by  the  lungs  grows  less  and  less. 
This  shows  that  the  activity  of  the  cells  has  diminished 
because  the  proi)er  supply  of  oxygen  is  not  furnished. 

Such  a  condition  soon  results  in  weakness,  and  makes 
the  body  an  easy  prey  to  disease. 

Ventilation. — Ventilation  is  a  process  by  which  the 
air  in  an  enclosure  is  removed  and  fresh  air  brought  in 
to  take  its  place. 

When  the  air  contains  over  .06  per  cent,  of  carbon 
dioxide  (from  breath)  it  is  unfit  for  breathing.  The 
carbon  dioxide  alone  is  not  so  objectionable,  for  one  may 
safely  breathe  air  containing  a  much  larger  per  cent,  of 
it.  But  along  with  carbon  dioxide  from  the  lungs  always 
comes  a  quantity  of  organic  poisons,  which  are  the  chief 
cause  of  impurity  in  the  air  of  living-rooms  and  in  halls 
where  people  meet. 

It  is  easy  to  determine  approximately  the  quantity  of 
carbon  dioxide  in  the  air,  and  this  can  be  taken  as  an  in- 


RESlMUATlOxN  181 

dication  of  the  quantity  of  other  impurities  if  all  came 
from  the  lungs. 

A  lamp  may  give  off  more  carbon  dioxide  to  the  air 
than  a  man  does  in  tlie  same  time,  and  yet  not  vitiate  the 
air  as  much. 

The  purpose  of  ventilation  is  to  supply  air  in  such  a 
condition  that  every  inhalation  will  supply  the  proi)er 
quantity  of  pure  oxygen  to  the  blood,  and  every  exhala- 
tion will  remove  a  pro'portionate  amount  of  waste. 

Fresh  air  must  be  admitted  into  the  room  where  i^eople 
stay  for  any  length  of  time  ;  otherwise  the  fire  of  life  is 
sure  to  burn  low.  Man  does  not  have  appetite  for  fresh 
air  as  he  has  for  food,  but  notice  of  bad  air  is  given  by 
drowsiness,  headache,  inability  to  study,  and  pallor  of 
the  skin. 

The  sense  of  smell  will  also  serve  as  a  guide  to  one 
coming  in  from  the  fresh  air. 

To  keep  the  air  fit  for  respiration,  3000  cubic  feet  of 
fresh  air  should  be  supplied  to  each  person  every  hour. 

Methods  of  ventilation.— Ventilation  is  ordinarily 
an  easy  matter  in  summer  time,  when  doors  and  windows 
may  stand  open.  But  in  cold  weather,  when  the  air  in 
the  room  nnist  be  kept  warm,  there  is  great  danger  that 
the  same  air  may  be  breathed  over  and  over. 

Many  private  houses  and  public  buildings  are  venti- 
lated with  a  constant  stream  of  fresh  warm  air,  which  is 
brought  in  from  pure  sources  on  the  outside  and  passed 
over  a  furnace  or  hot  coils  before  it  enters  the  room. 

This  plan  may  be  more  expensive  than  some  other 


182 


THIED    BOOK    OF   PHYSIOLOGY 


methods,  but  if  it  is  properly  constructed  and  oj^erated, 
it  will  save  doctor  bills,  and  will  increase  the  earning 
capacity  of  those  who  are  thus  supi:>lied. 

Steam  and  hot-water  radiators  placed  in  a  room  will 
heat  the  air  and  cause  it  to  move  about  by  convection 
icithin  the  room,  but  will  not  provide  ventilation. 


..£^1. 


m 


.  o  o  o  o  o  o  < 


lOOoOOOOO    o 


OOOOOOOOOO   oooooooocooo 
DOOOOOOOOOOO.OOOOOOOOOOC 

oooooooooooooooooooooo 


Fig.  87. — Window  arranged  for  ventilation. 


A  stove  or  fireplace  connected  to  a  chimney  that 
^'draws''  well  will  remove  a  considerable  quantity  of  air 
from  a  room^  and  fresh  air  will  come  in  through  the 
cracks  at  doors  and  windows.  This,  however,  will  not  be 
sufficient  except  for  one  or  two  persons. 

A  good  plan,  where  special  means  of  ventilation  have 


RESPIRATION  183 

not  been  provided,  is  (o  rais«i  the  lower  siush  of  ;i  window 
a  distance  of  three  or  four  inches  and  place  beneath  it  a 
board  or.  better,  a  perforated  zinc  box.  The  zinc  l)ox 
shonld  be  about  one  inch  thick,  three  inches  wid(^,  and 
jnst  long  enough  to  fit  in  beneath  the  sash.  The  perfo- 
ration in  the  two  sides  should  not  be  opposite.  In  this 
way  fresh  air  will  be  admitted  between  the  sash,  and 
other  air  will  go  out  through  the  holes  in  the  zinc  with- 
out causing  a  draft  in  any  part  of  the  room. 

Sleeping-rooms  need  special  care.  It  is  better  to  sleep 
in  a  cold  room  in  winter  time,  for  then  the  necessary 
covers  for  the  night  will  be  needed  at  once  on  retiring, 
and  windows  may  be  freely  opened.  Sound  sleep  is  not 
possible  in  bad  air. 

Good  breathing. — Though  one  may  be  supplied 
with  fresh  air,  he  may  not  get  the  full  benefit  from  it 
unless  he  breathes  it  to  the  blood  in  plentiful  quantity. 

Tight  clothing  about  the  waist  displaces  the  liver, 
stomach,  lungs,  and  other  organs.  This  not  only  gives  to 
the  body  a  deformed  appearance,  but  makes  free  respira- 
tion impossible. 

After  all  proper  conditions  are  complied  with,  it  is  still 
necessary  for  each  person  to  make  a  business  of  breathing 
for  a  short  time  each  day. 

This  may  be  done  in  the  country  or  park,  on  the  i>orch, 
or  in  a  room  before  an  open  window. 

A  good  exercise  of  this  kind  is  one  where  the  person 
stands  erect,  expands  the  chest  to  its  fullest  capacity, 
then,  holding  the  breath,  pushes  with  all  the  might  with 


184  THIRD   BOOK   OF   PHYSIOLOGY 

ODe  hand  against  the  wall  for  a  few  moments,  stands  erect 
again,  exhales,  then  fills  the  lungs  once  more  and  pushes 
with  the  other  hand. 

This  may  be  repeated  till  one  is  slightly  dizzj'.  In  a 
few  days  the  exercise  can  be  prolonged.  Such  breathing 
will  not  only  furnish  warmth  and  vigor  for  a  winter  day, 
but  will  greatly  diminish  liability  to  colds. 

Dust  in  air. — The  appearance  of  air  gives  but  slight 
indication  of  its  fitness  for  breathing.     Air  always  con- 
tains   a    large    number   of 
particles  which  are  not  vis- 
ible to  the  naked   eye  ex- 
^■■■:'\i->''Sj''^r^:/^:^-  cept   under  special  condi- 

tions, as  when  a  beam  of 
light  is  admitted  into  a 
darkened  room. 

Fig.  88  shows  some  dust 
particles    as   seen  through 
Fig.  88.— Particles  of  dust  from      a   high-power   microscope. 

a  living-room,  magnified.  rj.^^^^  ^^^  ^^^.^  ^  ^^^  ^^^^^ 

in  the  air  of  dwelling-rooms, 
and  consist  of  a  variety  of  particles  of  dead  matter  as 
well  as  living  germs. 

The  particles  are  very  minute,  but  exceedingly'  nu- 
merous. A  careful  count  has  shown  that  in  country  air 
there  are  about  100,000  particles  in  everj^  cubic  inch, 
and  in  towns  there  are  from  1,000,000  to  50,000,000  in 
a  cubic  inch. 

It  is  not  possible  to  avoid  all  dust   particles,  and  so 


KESIMUATION  185 

provision  is  iniide  in  the  iiir-pussages  to  prevent  their 
accuniuhition  in  tlie  hmgs,  ;is  lias  already  been  ex- 
plained. 

Dusty  air,  liowever,  should  be  avoided  as  far  as  pos- 
sible, not  only  because  the  dust  itself  is  objectionable, 
but  also  because  of  the  j^ernis  of  disease  which  are  liable 
to  be  i^resent  in  larger  numbers  when  dust  is  plentiful. 

Living  germs  in  the  air. — About  one  out  of  every 
seven  deaths  in  civilized  countries  is  caused  by  consump- 
tion of  the  lungs.  This  disease  is  aptly  called  the  '^  great 
white  plague.''  In  all  cases  it  is  caused  by  breathing 
into  the  lungs  the  living  germs  which  cause  that  disease. 
There  they  multiply  and  destroy  the  lung  tissue. 

There  is  no  danger  of  contracting  ' '  consumi)tion, ' '  or 
tuberculosis  of  the  lungs,  if  the  air  is  free  from  tubercu- 
lar germs. 

The  careless  spitting  of  a  consumptive  may  result  in 
a  spread  of  his  disease  to  others.  The  sputum  may  dry 
in  the  room  or  on  the  street,  and  then  be  blown  about 
with  the  dust.  The  germs,  though  dry,  will  live  for  a 
long  time  in  a  dormant  state.  As  soon  as  they  fall  upon 
a  spot  where  they  can  get  moisture  and  food,  they  become 
active  and  increase  in  number. 

Old  wall  paper  and  carpets  maj^  have,  clinging  to  them, 
many  germs  of  this  and  other  kinds.  To  sweep  such 
carpets,  or  dust  such  walls,  only  sets  afloat  the  dust  and 
germs.  The  occupants  of  the  room  are  then  compelled 
to  breathe  them,  or  the  dust  is  allowed  to  settle  upon 
the  books,  chairs,  tables,  and  clothes  in  the  room,  and 


18G  THIRD    BOOK    OF    PHYSIOLOGY 

will  be  afterwards  stirred  uj^  by  every  movement  in  the 
room.  Careful  dusting  with  a  moist  cloth  is  good,  but 
is  not  sufficient. 

Ordinary  house-cleaning  may  remove  the  dirt  which 
can  be  seen,  but  such  dirt  is  often  the  least  objectionable 
from  a  sanitary  point  of  view.  A  room  which  has  long 
been  in  use  as  a  living  apartment  cannot  be  cleaned 
unless,  in  addition  to  the  ordinary  means,  it  be  thoroughly 
fumigated.  This  should  be  done  at  least  once  each  year, 
whether  germs  of  contagion  are  known  to  be  present  or 
not. 

A  formaldehyde  generator  used  according  to  direc- 
tions will  effectively  cleanse  a  room  of  disease  germs, 
without  injury  to  the  furnishings  in  the  room  and  with 
little  expense  or  inconvenience. 

Effect  of  alcohol. — Every  one  is  liable  to  disease  at 
all  times.  Good  health  depends  largely  upon  ones  ability 
to  resist  disease.  Good  health  may  be  defined  as  that 
condition  in  which  the  oxv2:en  and  the  food  unite  in 
proper  quantity  to  produce  the  available  energy  needed 
by  the  body,  without  any  interference  from  poisons. 

As  already  explained  under  '^Circulation,"  alcohol 
does  interfere  by  extracting  oxygen  from  the  red  cor- 
puscles, and  the  heat  given  off  by  its  oxidation  is  more 
than  offset  by  the  derangements  of  the  organs  of  the 
body. 

The  effect  of  alcohol  is  not  always  apparent,  but  it 
always  interferes,  to  some  extent,  with  the  normal  proc- 
esses within  the  body. 


in^:spiij.\Tic)N  187 

A  wojikeiied  condition  of  any  part  of  the  body  makes 
tlio  wliole  body  liable  to  disejuse. 

A  larpfe  proportion  of  those  who  go  to  hospitals  because 
of  diseases  of  the  throat  and  lungs,  are  those  wlio  have 
been  addicted  to  the  use  of  alcohol. 

Continued  use  of  large  quantities  of  alcohol  cause  the 
lungs  to  become  congested  with  blood,  so  that  less  air  is 
breathed  into  them.  This  results  in  inllammation  and 
loss  of  vitality,  with  th6  consequent  inability  to  resist 
disease. 

Tobacco  smoke. — The  smoke  of  tobacco  irritates 
and  infiames  the  mucous  membrane  of  the  respiratory 
tract.  Those  who  smoke,  especially  those  who  inhale 
tobacco  smoke,  are  particularly  liable  to  catarrhal  in- 
flammation and  colds  in  the  head. 

The  most  injurious  effect  of  tobacco  results  from  the 
use  of  the  cigarette.  This  is  not  because  the  cigarette 
contains  more  injurious  substances  than  other  tobacco, 
but  because  of  the  way  it  is  used.  All  cigarette  smokers, 
except  the  merest  novice,  inhale  the  smoke  deep  into  the 
air-sacs  of  the  lungs.  It  was  shown  on  page  178  how 
easily  a  gas  can  transfuse  from  the  air-sac  into  the  blood. 
After  a  few  whiffs  and  inhalations  from  a  cigarette,  the 
effect  of  the  poison  can  be  felt  even  to  the  tips  of  the 
fingers  and  toes. 

The  use  of  the  cigarette  has  an  evil  effect  upon  men  of 
any  age. 

A  boy  cannot  select  a  more  effective  way  of  stunting 
his  growth  and  weakening  both  body  and  mind. 


188  THIRD    BOOK    OF    PirVSloLOGY 

QUESTIONS  FOR  REVIEW. 

1.  Describe  the  atmosphere. 

2.  In  what  sense  does  man  live  beneath  the  surface  of  the  earth  ? 

3.  How  is  man  dependent  on  the  air  ? 

4.  Define  respiration. 

5.  What  two  kinds  of  respiration  ?     Define  each. 

6.  Wliy  does  man  need  special  organs  of  respiration? 

7.  Of  what  use  is  oxygen  to  the  body  ? 

8.  "UTiere  in  the  body  does  oxygen  combine  with  food? 

9.  Name  all  organs  concerned  in  breathing. 

10.  Why  should  air  be  breathed  through  the  nostrils? 

11.  Describe  the  larynx  and  the  vocal  cords. 

12.  How  is  the  trachea  constructed? 

13.  Why  are  animals  choked  by  swallowing  a  large  morsel  of 
food? 

14.  Describe  the  ciliated  cells  in  the  trachea.     Of  what  use  are 
they  ? 

15.  What  are  the  bronchi  ? 

16.  What  are  bronchial  tubes  ?     Infundibula? 

17.  Describe  the  lungs  as  to  location,  weight,  density,  and  com- 
position. 

18.  What  is  the  pleura?     Of  what  use  is  it? 

19.  What  causes  air  to  move  into  the  lungs? 

20.  Does  the  air  expand  the  chest,  or  does  the  air  go  in  because 
the  chest  gets  larger  ? 

21.  Explain  the  action  of  the  ribs  in  inhalation. 

22.  How  does  the  diaphragm  cause  inhalation  ? 

23.  Construct  an  apparatus  to  illustrate  how  the  elevation  of  the 
ribs  will  increase  the  capacitv  of  the  chest. 

24.  What  forces  the  air  out  of  the  lungs  ? 

25.  How  is  air  forced  out  in  case  of  coughing  and  loud  speaking? 

26.  What  is  the  capacity  of  the  lung.-? 

27.  How  much  air  can  one  breathe  out  in  <jne  breath?- 


KKSPllJArioN  189 

2S.  Why  can  one  not  breathe  out  all  the  air  in  tin-  liingH? 

I**.!.   How  much  air  i.s  breathed? 

;;0.   What  is  the  C()nii)osition  of  air? 

."51.  What  i.s  the  most  important  gas  in  tiie  air,  and  how  can  its 
great  activity  be  demonstrated? 

.'>2.   What  is  meant  ))y  saying  tliat  air  is  a  mixture? 

."»:;.  What  is  the  use  of  nitrogen  and  argon  ? 

o4.  Of  what  use  is  carhon  dioxide  in  tiie  air?  W'ii.ii  are  lis  chief 
sources  ? 

35.   How  are  vegetables  and  animals  dependent  on  each  other? 

?A\.  AVhat  are  the  two  chief  objects  in  breathing? 

37.  Explain  the  osmosis  of  gases. 

38.  AVhat  is  the  composition  of  expired  air? 

30.  Compare  food  and  breathing  of  man  to  coal  and  draft  of  an 
engine. 

40.  Where  is  impure  air  found?     What  causes  it  to  be  impure? 

41.  Why  does  breath  make  it  impure? 

42.  What  is  ventilation? 

4?>.  What  is  the  purpose  of  ventilation  ? 

44.  How  can  impure  air  be  detected? 

4-3.  Describe  various  methods  of  ventilation. 

4<).  Why  is  a  steam-radiator  in  a  room  not  a  good  ventilator? 

47.  Describe  a  method  oi  window  ventilation. 

48.  Describe  a  breathing  exercise. 

49.  How  much  dust  is  in  the  air? 

50.  AVhat  becomes  of  the  dust  we  breathe  ? 

51.  How  is  lung  consumption  contracted? 

52.  AVhen  is  a  room  dean  ? 

53.  How  does  alcohol  interfere  with  respiration? 

54.  AA'hy  do  drinkers  more  easily  contract  disease? 

55.  How  does  smoking  affect  the  respiratory  tract? 

EXPERIMENTS. 

Burning  an  iron   wire  in  oxygen.— Fi{<.  8o  of  the  text  is  a  i>hoto- 
graph  of  the  burning  of  an  iron  wire  in  oxygen.     For  this  experimeirt  procure 


190 


THIED   BOOK   OF   PHYSIOLOGY 


a  large  granite-ware  spoon,  and  fill  it  full  of  pulverized  potassium  chlorate 
(KClOv).  Hold  the  spoon  over  a  Bunsen  flame  or  large  alcohol  lamp  till  the  po- 
tassium chlorate  is  all  in  a  liquid  form.  Have  ready  a  piece  of  picture-cord 
about  twelve  inches  long  Avith  one  end  slightly  frayed  out.  Heat  this  end  of  the 
wire  in  the  flame,  and  dip  it  at  once  into  some  sulphur.  "While  the  sulphur  ad- 
hering to  the  wire  is  burning,  hold  it  close  to  the  surface  of  the  liquid  in  the 
spoon.  Keep  the  spoon  over  the  flame.  The  iron  wire  will  burn  with  the  brill- 
iant scintillation  observed  in  the  photograph. 

Osmosis  of  gases.— Fig.  S6  shows  the  apparatus  needed  for  this  experi- 
ment. The  porous  cup  is  the  kind  ordinarily  used  in  battery  jars.  The  oi)en 
end  can  be  closed,  by  means  of  a  little  plaster  of  Paris,  through  which  passes 
a  glass  tube.    The  hydrogen  can  readily  be  prepared  by  pouring  some  dilute 

hydrochloric  acid  upon  some  zinc  in  a  bottle. 
Place  the  large  glass  jar  over  the  bottle  and 
collect  some  hydrogen.  After  one  or  two  min- 
utes, or  less,  lift  the  jar  to  a  piosition  over  the 
I)orous  jar,  and  watch  for  bubbles  in  the  water  at 
the  lower  end  of  the  glass  tube. 

Action  of  the  intercostal  muscles.— 
Between  the  ribs  are  two  sets  of  intercostal  mus- 
cles. In  one  set  the  fibres  run  obliquely  down- 
ward and  forward.  In  the  other,  upward  and 
forward.  When  the  first  contracts,  the  ribs  are 
raised.  The  contraction  of  the  second  set  de- 
presses them. 

This  may  be  illustrated  by  the  device  shown 

in   Fig.  89.      Four    pieces  of    wood  are   jointed 

together  in  the  manner  shown.    Tacks  are  driven 

into  the  horizontal  pieces  at  intervals  of  an  inch 

or  more.     These  two  strips   represent  two  ribs. 

Stretch  elastic  bands  between  the  tacks,  as  shown 

in  the  upper  part  of  the  figure,  and  their  elastic 

force  will  elevate  the  strips.    This  is  the  effect  of 

the  first  set  of  intercostal  muscles,  and  they  are 

employed  in  inhalation.     Now  arrange  the  bands  as  shown  in  the  lower  part 

of  the  figure,  and  the  strips  will  be  lowered.    This  is  the  action  of  the  second 

set  of  intercostals,  and  they  are  used  in  exhalation. 

Test  for  carbon  dioxide  in  the  breath.— Procure  a  piece  of  un- 
slaked lime  and  place  it  in  a  quart  jar,  nearly  full  of  water.    Shake  the  jar  occa- 


FiG.  89. — Apparattis  il- 
lustrating the  action  of  the 
intercostal  muscles. 


RESPIEATrON  191 

gionally,  and  sot  asuit'  till  the  linu'settU'.s  and  tlio  liijuid  l)ccoMies  rHjrffCtly  ck-ar. 
Decant  a  little  of  tlu-  clear  linuid  into  a  small  Ixittle  or  a  test-tuhe.  iJlow  air 
from  the  hintrs  through  a  tnK'  into  the  lime  water.  The  water  will  lieeome 
milky  white.  The  carhon  dioxide  has  unitt'd  with  the  lime,  and  formed  cal- 
cium carbonate,  which  hangs  in  small  particles  in  the  water. 

To  test  the  ventilation  of  a  room.— Prepare  some  touch-pa[»er  by 
soaking  any  kind  of  soft  j'aper  in  a  solntion  of  .saltpetre.  After  the  paix-r  is  dry 
it  can  be  lighted,  and  will  continue  to  smoke,  but  will  not  burn  with  a  flame. 

By  use  of  the  smoke  from  a  taper  made  of  such  paper,  test  the  doors,  win- 
dows, and  other  points  where  air  may  enter  or  leave  the  room  where  you  live. 

Raise  the  lower  sash  just  a  little,  and  determine  whether  air  is  coming  in  or 
going  out,  above  and  below  the  sash.  Each  one  should  do  this  at  his  own 
home. 


CHAPTEE    XII 


BACTERIA 


What  bacteria  are. — Bacteria  are  a  class  of  very 
minute  i^lants.  During  the  last  t^renty  years  they  have 
been  studied  very  closely,  and  are  found  to  be  very  use- 
ful agents  in  every-day  life. 

They  are  able  to  bring  about 
changes  in  nature  without  which 
neither  plants  nor  animals  could 
long  continue. 

They  are  of  use  in  the  manufac- 
turing industries  and  in  the  pro- 
duction of  articles  of  food. 

They  also  cause  many  of  the  dis- 
eases from  which  man  and  the  other 
animals  suffer. 

A  scientific  study  of  these  minute 
organisms  is  called  bacteriology. 

Fig.    90.  —  Bacteria.  --,  ,      .  j?  -l       x       • 

A,  spheres ;  B,  rods ;  c,        Shape  and  size  of  bacteria. 

spiral.^.  — There  ai  e  many  different  kinds  of 

bacteria,  but.  as  far  as  their  shape 
and  size  are  concerned,  there  are  only  three  clas.ses, — 
the  spheres,  the  rods,  and  the  spirals.  The  characteristic 
shapes  are  shown  in  Fig.  90.  The  spheres  may  vary  in 
size,  but  all  are  very  minute.  If  lUO.OUO  of  the  largest 
192 


HACTKRIA 


193 


of  them  were  placed  in  a  line  side  by  sid<',  the  line  wonld 
be  only  six  inches  lon«^. 

The  rods  are  very  narrow,  bnt  some  kinds  have  con- 
siderable length. 

The  spirahs  are  similar  to  the  rods  in  size. 

Bacteria  are  the  smallest  living  things  that  have  ever 
been  seen  in  a  microscoi)e. 

How  they  multiply. — The  great  number  of  bac- 
teria and  the  rapidity  with  which  they  can  multiply 
make  them  very  important  agents  in  the  world  for  good 
or  evil. 

They  increase  in  number  by  a  division  of  one  into 
two.  two  into  four,  four  into  eight,  and  so  on. 


Fig.  91.  —  Multiplication  liv  divi.-ion. 

A  sphere,  as  seen  in  Fig.  01,  will  become  elongated, 
and  finally  divide  in  the  middle  and  become  two. 

All  bacteria  multiply  in  this  way.  In  this  respect 
they  differ  from  yeast  germs,  which  multiply  l)y  a  method 


Fig.  92. — Yeast-plants. 

called    huddhuj.     Yeast    germs   are    shown    in    Fig.  92. 
This  is  the  chief  mark  of  distinction  between  yeast  and 

bacteria.- 

13 


194  THIED   BOOK    OF   PHYSIOLOGY 

Tlie  rapidity  of  multiplication  of  bacteria  depends  on 
many  conditions,  such  as  temperature,  moisture,  and 
the  amount  of  food  which  the  bacteria  can  get.  Some 
can  double  their  number  every  thirty  minutes.  At  this 
rate  it  is  easy  to  calculate  that  a  single  bacterium  would 
in  twelve  hours  have  increased  in  number  to  more  than 
8,398,000. 

The  food  of  bacteria. — Bacteria  are  defined  as 
plants,  and  yet  in  some  respects  they  are  like  animals. 
Plants  live  on  food  of  a  very  simple  kind,  which  they 
can  make  into  complex  forms  suitable  for  the  food  of 
animals.  Bacteria  in  this  respect  are  like  animals,  for 
they  live  only  on  complex  foods,  and  can  live  and 
thrive  only  when  they  can  get  it.  For  this  reason  it  is 
dangerous  to  allow  certain  bacteria  to  get  a  lodgement  in 
the  tissues  of  the  body,  for  there  they  find  the  kind  of 
food  they  want,  and  so  will  multiply  and  produce  poi- 
sons which  are  the  cause  of  many  diseases. 

Where  bacteria  are  found. — Bacteria  are  found 
in  every  place  where  animals  and  plants  live.  The  soil 
is  full  of  them  to  a  depth  of  two  or  three  feet  or  more. 
They  are  in  all  bodies  of  water.  All  decaying  matter  is 
crowded  with  them.  Animals,  including  man,  contain 
them  throughout  the  whole  alimentary  tract.  They 
cling  to  the  skin  and  the  clothes.  Any  disturbance  that 
will  raise  a  dust  in  a  room  or  on  the  street  will  cause 
great  numbers  of  them  to  float  in  the  air. 

They  are  not  found  in  the  tissues  of  any  healthy 
orsran. 


BACTKIMA  195 

Use  of  bacteria  in  the  industries.— Mauy  tliou- 
sands  of  dollars  are  invested  in  industries  wliicli  ai'e  de- 
pendent on  the  help  of  bacteria.  Bacteria  are  able  to 
bring  abont  many  useful  chemical  changes.  For  ex- 
ample, when  cidei"  is  allowed  to  stand  in  air  it  soon  be- 
comes sour  and  is  changed  to  vinegar.  If  the  cider  had 
been  boiled  and  then  sealed  from  the  air,  it  would  liave 
remained  fresh. 

The  change  to  vinegar  is  caused  by  bacteria,  which 
find  in  cider  a  desirable  food.  The  x^roduct  of  their  life 
there  is  the  vinegar.  The  ''mother  of  vinegar"  is  a 
mass  of  millions  of  bacteria. 

Other  kind  of  bacteria  find  milk  a  suitable  food.  One 
product  of  their  life  is  an  acid  which  makes  the  milk 
sour  and  causes  it  to  curdle.  Milk  would  remain  sweet 
indefinite!}^  if  bacteria  could  be  kept  out  of  it. 

The  flavor  of  butter  is  due  to  the  work  of  bacteria,  and 
the  ripening  of  cheese  is  also  a  result  of  changes  which 
they  bring  about. 

The  •'retting"  of  flax,  by  which  the  tough  fibres  of 
linen  are  separated  from  the  woody  part,  is  effected  by 
bacteria. 

Thus  it  is  possible  to  name  many  arts  in  which  bac- 
teria play  an  important  part.  Enough  has  been  said  to 
show  that  these  minute  organisms  are  not  always  an 
enemy  of  man.  In  fact,  most  of  them  are  not  only  harm- 
less, but  a  great  aid. 

It  is  man's  duty  to  find  out  their  character  and  habits 
of  life  and  turn  them  to  good  use. 


196  TRIED    BOOK   OF   PHYSIOLOGY 

Bacteria  as  food  producers. — The  material  of  our 
food  is  used  over  and  over.  Plants  change  simple  com- 
pounds into  complex  ones,  such  as  proteids,  fats,  and 
carbohydrates.  Plants  cannot  live  on  these.  The  car- 
bon dioxide  which  the  animals  breathe  out  is  a  suitable 
food  for  plants.  Plants  cannot  live  on  the  tissues  of  ani- 
mals or  i^lants  until  they  are  broken  up  into  simple 
comi)Ounds. 

This  is  the  work  of  bacteria.  When  an  animal  dies  in 
the  field  or  a  tree  falls  in  the  woods,  their  bodies  soon 
soften  and  decay.  This  is  the  result  of  the  work  of  mill- 
ions of  bacteria,  whicli  find  there  the  complex  foods 
upon  which  they  thrive.  The  tissues  are  thus  reduced 
to  simi^le  compounds  suitable  again  for  i^lant  life. 

If  no  bacteria  are  present,  meat  will  not  spoil  and 
plants  will  not  decay. 

Thus  the  same  material  may  go  round  and  round, 
from  air  and  soil  to  plants,  from  plants  to  animals,  from 
animals  through  bacteria  back  to  plants  again. 

The  energy  comes  from  the  sunlight,  and  as  long  as 
the  sun  shines  upon  green  leaves  this  circuit  of  food 
material  may  continue. 

Yeast. — Y'east  germs  are  classified  as  different  from 
bacteria,  for  reasons  given  on  page  193.  But  thej^  are 
microscopic  plants,  and  can  produce  great  chemical 
changes  in  the  substances  in  which  the}-  can  live  and 
multiply. 

The  chief  products  of  their  life  are  alcohol  and  carbon 
dioxide.     The  process  by  which  this  is  done  is  called 


BACTKIMA  197 

fermentation,   and    tliis    lias   already  been    explained    in 
Chapter  IX. 

The  fermentation  caused  by  the  yeast-plant  is  the  fii-st 
step  in  the  disinti'gration  of  many  substances.  Aft^r 
the  work  of  the  yeast-i^lant  is  done,  certain  bacteria  may 
enter  the  substance  and  make  other  changes  until  the 
simple  forms  of  plant  food  are  produced. 

Bacteria  which  produce  disease. — Probably  all 
bacteria  are  of  some  great  use  in  the  world.  M<jst  of 
them  are  harmless  to  man.  A  few  species,  however,  can 
live  and  multiply  in  the  tissues  and  in  the  alimentary 
tract  of  the  bodj.  There  they  j)roduce  violent  poisons, 
which  are  the  cause  of  serious  sickness,  which  often 
results  in  death.  Bacteria  themselves  are  not  so  danger- 
ous, but  the  violent  poisons  thej^  produce  are  taken  up 
by  the  blood  and  distributed  through  the  body. 

Cholera  infantum.  —  KSome  germs,  already  de- 
scribed as  i)leutiful  in  milk,  continue  to  live  after  the 
milk  is  taken  into  the  stomach.  The  effect  on  infants  is 
a  disease  called  cholera  infantum.  The  effect  is  not  so 
noticeable  on  those  who  are  older  and  less  delicate. 

These  bacteria  do  not  enter  the  tissues  of  the  body, 
but  onh"  continue  to  live  in  the  milk  after  it  is  swal- 
lowed. 

The  projjer  precautions,  particularly  in  warm  weather, 
is  to  use  only  milk  which  has  l)een  sterilized. 

Diphtheria. — The  bacteria  which  cause  diphtheria 
act  only  on  the  mucous  membrane  of  the  throat.     There 


198  THIRD    BOOK    OF   PKYSIOLOGY 

they   cause  a  whitish  membrane   to   form,   which  may 
close  the  air-passages. 

Here  they  produce  a  violent  poison  wliich  is  absorbed 
into  the  body.     The   germs  which  produce  this  dread 

disease  may  easih^  be  con- 
«5-p.^%:^  veyed  from  one  person  to 

^r?^*^^'^/^  another.     The   only  safety 

*^-     "^•^»^-  is  in  the  complete  isolation 


m-<r  i  ^-m^aa  ^jf  the  patient  and  all  who 

S  V^  i*^  live  in  the  same  house  until 

Fig.  03.-Germs  of  diphtheria,      the  germs  are  all  killed  by 
Klebs-Loeffler  bacilli,  from  speci-     the  application  of  a  germi- 
mens  prepared  hv  Dr.  Coplin  and         •  •, 
Dr.  Bevan.     Fresh  culture  upon 

blood    serum.       Eye-piece     IV..  Physicians  are  now  treat- 

Beck;  Objective  J^oLim.  (Lei  tz.  j      ii^g    the    disease  with    suc- 
This  is  also  the  appearance  when  .        .    .      _  ,  •        , . 

obtained  directly  from  the  throat       ^^^'^^  "^^  mjectmg    mto   the 
and  subjected  to  the  same  power.       blood  of  the  patient  a  J^rep- 

aration  called  dijyhtheria  an- 
titoxin. It  is  obtained  from  the  l;)lood  serum  of  horses 
which  have  been  purposely  caused  to  have  the  disease. 

In  this  way  not  only  have  diphtheria  i:)atients  been 
cured,  but  those  who  were  exposed  to  the  disease  have 
been  made  immune  from  its  attack. 

Lock-jaw. — The  dreaded  disease  called  tetanus,  or  lock- 
jaw, is  caused  bj'  germs  which  have  the  appearance  shown 
in  Fig.  94.  These  germs  are  plentiful  in  the  soil,  and 
may  be  introduced  into  the  flesh  through  a  wound  in  the 
foot  or  in  many  other  ways. 

The  bacteria  themselves  are  confined  to  the  locality  of 


UACTKIMA  ]1>9 

the  wound.  Tlicro  they  j»i<«liu'('  a  \  iolent  ijoisoiu  wliicli 
is  taken  np  by  tlic  Mood.  Moir  tliaii  the  usual  nund)er 
of  cases  ol"  lock-jaw  ocenr  alter  each  Fourth  of  .Tnlj',  as 
a  result  of  the  admission  of  these  bacteria  into  wounds 
eans<Ml  ]>y  lir(^-era('k<'is  an<l  toy  pistols. 


Fig.  94. — Germs  of  lock-jaw. 

Tuberculosis. — Tuberculosis  is  caused  by  bacteria 
of  the  rod  shaped  kind.  This  disease  may  be  located  in 
various  i^laces  in  the  body,  but  is  commonly  found  in  the 
lungs.     There  the  bacteria  thrive  on  the  lung  tissue. 

It  was  once  supposed  that  tuberculosis  could  neither  be 
prevented  nor  cured.  Xow  it  is  known  that,  with  j^roper 
care,  both  prevention  and  cure  are  possible. 

It  is  not  possible,  in  most  localities,  to  avoid  breathing 
the  germs  ;  but  it  is  possible  to  have  such  healthy  lungs 
and  such  a  robust  body  that  they  cannot  gain  entrance  to 
any  part  of  the  lung  tissue. 

The  contraction  of  colds  that  •'■settle"  in  the  throat  or 


200  THIED   BOOK   OF   PHYSIOLOGY 

on  the  lungs,  furnishes  favorable  conditions  for  the  germs 
of  pneumonia  and  consumption.  If,  in  addition  to  this, 
the  body  be  poisoned  by  the  inhalation  of  cigarette  smoke 
and  the  drinkiug  of  alcohol,  the  body's  power  of  resist- 
ance is  also  greatly  weakened. 

It  is  plainly  shown  that  one  who  has  a  weak  constitu- 
tion, or  one  who  is  already  suffering  from  some  affection 
of  the  lungs,  may  readily  contract  tuberculosis  from 
others  who  have  the  disease. 


/'^     .        k/^\.      \J 


( 


>^        V^     ^ 


y^ 


Fig.  95. — Germs  of  tuLerculosis. 

The  two  fundamental  precautions  in  reference  to  this 
disease  are,  a  vigorous  state  of  health,  and  avoidance  of  con- 
tamination from  others. 

Laws  of  public  health  require  that  association  with  con- 
sumptives be  avoided.  This  is  particularly  so  in  public 
places  and  close  rooms. 

Because  this  disease  is  not  violent,  but  slow  and  insidi- 
ous, people  become  careless  in  regard  to  it,  though  it  is 
known  to  kill  about  15  per  cent,  of  the  human  race. 


BA(TKIMA  201 

Typhoid  fever. —  In  Fig.  9G  are  shown  the  bacteria 
which  are  the  cause  of  tjfphoid  fever.  These  grow  in  the 
intestines,  but  also  often  spread  to  the  liver  and  other 
ghmds.  They  can  move  about  by  motion  of  the  minute 
projections  called  Jlagella.  Poisons  which  they  produce 
are  the  cause  of  the  violent  fever  which  is  characteristic 
of  this  disease. 

These  germs  are  conveyed  chiefly  by  food  and  water. 
The  water  of  a  single  Well  has  often  been  the  cause  of  an 


■^ 


1^- 


^^-     -  ^^"j^ 

"r^ 


t  r    -<- 


ir    ^' 


Fio.  06. — Typhoid  fever  germs. 

epidemic  of  typhoid  fever.  A  shallow  well  is  always  to 
be  suspected  on  this  account. 

Provisions  in  the  body  for  resisting  bacteria. 

— We  have  mentioned  only  a  few  of  the  diseases  which 
are  caiLsed  by  bacteria.  There  is  a  constant  contest  for 
supremacy  between  the  living  cells  within  the  body  and 
the  living  cells  (bacteria)  without. 

The  cells  within  are  an  organized  body,  and  are,  as  it 


202  THIRD   BOOK   OF   PHYSIOLOGY 

were,  fortified  in  their  place  ;  but  the  bacteria  possess 
means  of  attack  which  are  often  successful  if  the  fortifica- 
tions are  weak. 

The  body's  chief  means  of  protection  are  the  skin,  cer- 
tain coiuiter-poisom  which  destroy  or  check  the  growth  of 
bacteria,  and  the  white  corpuscles. 

The  skin  as  a  protection. — Tlie  skin  may  be 
likened  to  a  strong  wall  about  the  organized  body  of  cells 
within.  Bacteria  may  hang  in  great  numbers  on  the  out- 
side of  the  skin,  but  they  cannot  go  through  it.  The 
linings  of  the  respiratory  and  alimentary  tracts  act  as  a 
similar  protection  against  most  germs. 

When,  however,  a  bruise,  cut,  or  mixture  of  any  kind 
occurs  in  these  protective  coverings,  the  bacteria  at  once 
invade  the  tissues.  Even  a  slight  scratch  of  the  skin 
may,  for  this  reason,  become  a  bothersome  wound. 

Surgeons  now  know  how  to  dress  a  wound  so  that  bac- 
teria are  kept  away.  The  wound  then  heals  rapidly  and 
without  the  formation  of  pus. 

Alexines. — It  is  not  possible  to  prevent,  at  all  times, 
the  access  of  bacteria  into  the  living  tissue.  Fortunately, 
however,  certain  substances  in  the  blood  and  tissue 
make  most  bacterial  life  impossible  there.  They  are 
called  alexines.  Although  their  nature  is  not  well  known, 
it  is  clear  that  they  serve  as  protective  agents  against 
bacteria. 

Certain  disease-producing  bacteria  are  able  to  neu- 
tralize the  action  of  the  alexines,  and  so  proceed  to 
establish  themselves  in  the  living  tissue. 


IU(Ti:iilA  208 

The  white  corpuscle. — AftiM-  llu-  ordinary  moans 
h;i\o  failed  to  repel  the  invading  baeteria,  the  body  still 
has  in  reseiNc  another  means  <►!'  defence.  One  of  the 
chief  dnties  of  the  white  corpuscle  is  to  go  abont  throngh 
the  body,  apparently  in  search  of  foreign  bodies,  which 
they  at  once  attempt  to  remove  or  render  harmless. 
They  are  not  confined  to  the  blood-vessels,  bnt  can  glide 
out  into  the  tissues.  They  can  take  into  their  bodies 
minute  particles  which  they  dissolve  or  carry  away  even 
if  they  must  sacrifice  themselves  in  doing  so.  For  this 
reason  they  are  often  called  the  scavengers  of  the  body. 

When  bacteria  gain  admission  to  the  tissue  at  any 
point,  as  through  a  wound,  the  white  corpuscles  gather 
there  in  great  numbers.  The  wound  becomes  swollen 
and  inflamed  because  of  their  presence.  They  appear  to 
pour  out  from  their  bodies  a  secretion  which  checks  the 
growth  of  bacteria.  Many  white  corpuscles  are  killed  in 
the  conflict,  and  the  accumulation  of  their  dead  bodies 
forms  the  substance  called  j^its. 

Some  bacteria  are  able  to  produce  such  violent  poisons 
that  the  white  corpuscles  are  not  able  to  check  them. 
In  such  cases  the  disease  will  ''run  its  course,"  and  the 
bacteria  would  continue  to  multiply  until  death  would 
result,  except  that  the  body  itself  then  produces  sub- 
stances which  are  an  antidote  to  the  bacterial  poisons. 
If  the  body  is  able  to  survive,  the  disease  will  reach  a 
climax  and  recovery  will  begin.  This  changed  condi- 
tion oft^n  renders  the  body  immune  from  an  attack  of 
the  same  diseiuse  for  a  certain  length  of  time.  Some- 
times for  a  lifetime. 


204  THIED   BOOK   OF   PHYSIOLOGY 

Argument  for  a  robust  body. — Many  things  in 
regard  to  bacterial  diseases  are  not  definitely  known. 
It  is  well  known,  however,  that  most  diseases  are  caused 
by  these  minute  organisms,  and  that  one  whose  body 
is  robust  and  whose  habits  of  life  are  good  can  most 
effectively  resist  their  attack. 

Drugs  are  effective  in  killing  bacteria  outside  the 
body,  but  no  drug  now  known  will  destroy  them  after 
they  are  lodged  in  tlie  living  tissue,  without  destroying 
the  body  as  well. 

The  effective  means  of  combating  them  comes  in  a 
natural  way  from  within  the  body  itself.  The  state  of 
the  body  determines  its  ability  to  resist  disease.  This  is 
a  good  reason  for  the  maintenance  of  a  body  in  which 
every  cell  is  assimilating  its  due  proportion  of  food  and 
oxygen,  and  performing  its  part  in  relation  to  the  welfare 
of  the  body  as  a  whole. 

Modern  discoveries  show  that  the  physician  may  assist 
the  body  in  its  effort  to  neutralize  the  bacterial  poisons. 
This  he  does  not  attempt  to  do  by  the  use  of  drugs 
intended  to  kill  the  germs,  but  by  injection  of  certain 
substances  which  will  make  the  poisons  harmless.  For 
examx)le,  one  who  is  bitten  by  a  mad  dog  is  almost  sure 
to  suffer  from  hydrophohia.  The  disease  does  not  develop 
for  some  time,  so  that  the  body  may  be  prepared  for  it 
before  it  sets  in.  The  physician  is  prepared  with  mate- 
rial taken  from  the  spinal  cord  of  a  rabbit  which  has 
died  from  the  disease.  This  is  injected  into  the  body 
of  the  patient,  first  in  a  mild  form  and  then  in  stronger 
and   stronger   doses.     When  the   disease   does  develop, 


BACTKiUA  20.') 

the  body  is  used  to  the  poisons  producod,  and  no  serious 
results  follow. 

QUESTIONS  FOR  REVIEW. 

1.  What  are  bacloriii,  uiul  what  do  they  do? 

2.  Describe  the  shape  and  size  of  bacteria. 

3.  How  do  bacteria  muhiply? 

4.  How  do  they  differ  from  the  yeast  germ? 

5.  On  what  kind  of  food  do  bacteria  subsist? 

6.  Why  do  some  kinds  of  bacteria  invade  the  tissues  of  the  body  ? 

7.  Where  can  bacteria  be  found? 

8.  Explain  the  formation  of  vinegar. 

9.  Name  several  arts  and  industries  in  which  bacteria  have  a 
part. 

10.  In  what  condition  must  the  food  of  plants  be?     Tlie  food  of 
animals? 

11.  How  do  bacteria  prepare  plant  food? 

12.  What  causes  meats  and  fruits  to  spoil? 

13.  What  is  the  source  of  the  energy  in  food? 

14.  What  is  the  cause  and  effect  of  fermentation  f 

15.  How  do  bacteria  produce  disease? 

16.  What  is  the  cause  of  diolera  infantum  f 

17.  What  is  diphtheria,  and  how  may  it  be  treated? 

18.  What  is  tetanus  ? 

19.  How   are   tubercular  germs   conveyed  from  one   person   to 
another? 

20.  How  can  consumption  be  avoided? 

21.  What    is    typhoid  fever?     How  is  it  carried  about  from  one 
to  another  ? 

22.  What  three  provisions  are  made  in  the  body  for  resisting 
bacteria  ? 

23.  How  does  the  skin  resist  bacteria? 

24.  What  are  alexines,  and  what  is  their  use? 

25.  How  do  white  corpuscles  resist  bacteria? 

26.  Give  a  good  reason  for  maintaining  a  robust  body. 


CHAPTEE    XIII 

THE     SKIN 

General  character  of  the  skin. — The  skin  is  a 
tough,  pliable,  and  elastic  covering  over  the  entire  out- 
side surface  of  the  bod3\  The  mucous  membrane,  which 
lines  all  cavities  of  the  body  that  communicate  with  the 
outside^  may  be  considered  a  continuation  of  the  outer 
skin,  though  much  modified  in  character.  The  hairs  and 
nails  are  only  modified  forms  of  the  skin.  The  claws, 
hoofs,  and  horns  of  animals  are  modified  forms  of  the 
skin  which  covers  their  bodies. 

Use  of  skin. — The  chief  function  of  the  skin  is  to 
serve  as  a  protective  covering.  AVe  have  already  de- 
scribed its  use  as  a  protection  against  the  invasion  of 
bacteria.  In  every- day  life  the  body  must  constantly 
come  in  contact  with  outside  objects,  and  a  strong  cover- 
ing like  the  skin  is  needed  to  protect  the  delicate  parts 
beneath. 

To  make  the  skin  a  more  effective  guardian  of  the  body, 
it  is  filled  with  terminals  of  nerves.  Thus  the  mind  is 
instantly  notified  when  any  part  of  the  body  comes  in 
contact  with  outside  objects. 

In  addition  to  its  use  as  a  protection,  it  also  serves  as 
an  excretory  organ.  A  great  deal  of  water  and  some 
waste  are  taken  from  the  blood  by  the  glands  in  the  skin. 
206 


TIIK    SKIX 


207 


The  evaiX)ration  of  the  water  from  the  surface  of  the 
skill  hits  an  important  nso  in  ro<rnhitin<^  tlio  temperature 
of  tlie  body. 

The  two  layers  of  the  skin. — The  skin  is  com- 
posed of  two  hiyers.  The  tuiter  one  is  called  the  ejri- 
dennis,  cuticle,  or  scarf-skin.  Just  beloNV  it  is  the  true 
skin,  also  called  the  demiis,  or  cutis. 


\n 


Fig.  07. — Cross-section  of  skin  from  the  finger  of  a  monkey. 
Photographed  through  a  microscope. 

Fig.  97  is  a  microphotograph  of  a  cross-section  of 
the  skin  from  a  monkey's  finger.  The  two  layers  can  be 
plainly  seen. 

The  epidermis. — The  epidermis  is  very  thin  on 
most  of  the  surface  of  the  body.     It  is  thicker  on  the 


208  THIRD    BOOK    OP^    PHYSIOLOGY 

palms  of  the  liauds  and  the  soles  of  the  feet.  It  may 
become  thick  at  any  point  where  there  is  continuous 
friction  or  rubbing.  In  this  way  ^'corns''  are  formed  on 
the  feet  by  ill-fitting  shoes. 

The  palms  of  a  workman's  hands  become  hard  from 
constant  pressure  on  the  handles  of  tools. 

Epidermis  is  formed  of  several  layers  of  jjavement  epi- 
thelium. (See  page  2-4.)  The  cells  composing  it  are  con- 
tinually supplied  from  beneath,  and  the  old  ones  are  as 
constantly  being  worn  away  or  drop  off. 

Y^^heu  a  blister  is  formed,  as  from  a  burn,  the  epidermis 
is  separated  from  the  dermis. 

Xo  blood-vessels  or  nerves  are  supplied  to  the  epider- 
mis. The  cells  of  its  deepest  layer  are  alive,  and  are 
nourished  by  the  lymph  which  they  absorb.  These  pro- 
duce the  cells  of  the  outer  layers,  which  gradually  dry  up 
and  become  cemented  together,  forming  the  horny,  trans- 
parent layer  which  covers  the  whole  surface  of  the  body 
and  protects  the  delicate  tissue  beneath. 

Color  of  the  skin. — The  deeper  layers  of  the  epider- 
mis are  supplied  with  granules  of  coloring  matter.  The 
amount  and  kind  of  granules  differ  greatly  in  different 
persons  and  different  races.  The  skin  of  albinos  is  entirely 
devoid  of  coloring  matter.  Xegroes  are  abundantly  sup- 
plied with  it.     A  brunette  has  more  of  it  than  a  blonde. 

Sunlight  makes  the  granules  darker.  An  uneven  dis- 
tribution of  the  granules  is  the  cause  of  frecMes. 

The  dermis  or  true  skin. — As  shown  in  Fig.  98, 
the  surface  of  the  true  skin   is  composed  of  numerous 


TUK    SKIN 


209 


rid«j:cs.  These  are  conical  projections  over  wliicli  the 
epidermis  is  closelj^  moiihled.  They  are  called  jxipillce. 
Some  of  them  are  filled  with  blood-vessels.  Othei-s  are 
terminations  of  nerves  of  touch.  The  dermis  is  plenti- 
fully supplied  with  blood  and  nerves. 

The  nerve  papilhe  are  numerous  all  over  the  surface  of 
the  body,  but  are  especially  numerous  in  those   places 


^— p 


9 


S    ■ 


Fig.  98. — A  magnified  cross-section  of  the  skin,  e,  epidermis  ;  p^ 
papillae ;  5,  sebaceous  gland  ;  r,  root  of  hair ;  /,  fat ;  7,  sweat-glands  ; 
a,  pores. 

where  they  can  be  of  greatest  service  to  the  body,  as  on 
the  tongue,  lips,  and  tips  of  the  fingers.     On  the  palms 
of  the   hands  thej'  are  arranged  in  rows,  thus  causing 
ridges  which  may  be  plainly  seen  with  the  naked  eye. 
As  may  be  seen  in  Fig.  98,  the  larger  part  of  the  dermis 

14 


210  THIRD   BOOK    OF   PHYSIOLOGY 

is  composed  of  interlaciug  bands  of  connective  and  elastic 
tissue.  These  make  the  skin  tough  and  at  the  same  time 
permit  it  to  be  stretched.  Beneath  the  skin  is  the  loose 
areolar  tissue  in  which  fat  is  dex)Osited,  giving  the  skin  an 
even  surface.  When  the  fat  is  used  up  by  the  body,  the 
skin  becomes  wrinkled  because  it  is  then  too  large  for  the 
part  which  it  covers.     In  the  regions  just  below  the  dermis 


Fig.  99. — From  the  surface  of  the  paha  of  the   hand.     The    ridges 
are  rows  of  papilhe.     The  dots  are  pores. 

are  numerous  sweat-glands  which  communicate  with  tlie 
surface  through  their  spiral  ducts. 

The  roots  of  hairs  reach  down  to  different  depths,  most 
of  them  beino^  in  the  fattv  laver.  At  the  sides  of  the 
hairs  are  oil-glands. 

Sweat-glands. — With  an  ordinary  magnifying  glass, 
a  great  number  of  minute  spots  can  be  seen  on  the  ridges 
of  epidermis  on  the  palms  of  the  hands.  These  are  the 
pores  of  the  sweat-glands.     They  are  found  in  all  parts 


TIIF.    SKIN  211 

of  (lie  surface  of  llu*  l>o<ly,  hut  arc  most  muiierous  on  the 
palms  and  soles.  It  lias  been  estimated  that  there  are  in 
all  about  2,r)()(),()0()  s\\eat-«,^lands. 

The  gland  is  a  long  tube,  closed 
at  one  end  and  coiled  up  as  shown  ^f^ 

in  Fiji:.  100.     Kound  about  this  coil         ^     ./'    ':        r^M 

are  numerous  blood  capillaries,  from  ''/ 

,  / 

which  the  gland   secretes  a   great         Jf'y  -, 

deal  of  water  and  some  waste  mat-         ^rM^^I^ 

ter,  and  i^ours  them  out  on  the  sur-         ^ 

face  of  the  body.  ^ 

Perspiration.— The   escape  of 

the  excretions  of  the  sweat-glands  ''^?^'^4' 

at  the  surface  of  the  skin  is  called   ^      ^r.c^     c-      ^    i     , 

Fig.  100. —Sweat-glands, 

jyersjnration.      It   may   take   j^lace 

rapidly,  making  the  skin  wet  with  sweat.  It  is  then 
called  sensible  perspiration  because  it  can  be  perceived  by 
the  senses. 

At  all  other  times  the  water  evai^orates  as  fast  as  it 
reaches  the  surface,  and  it  is  then  called  insensible  per- 
spiration. 

The  average  amount  of  water  persjjired  in  a  day  is 
about  one  quart. 

Insensible  perspiration  may  be  readily  shown  by  in- 
serting a  finger  into  a  cold,  dry  bottle  or  test-tube.  The 
inner  surface  of  the  glass  will  ''fog,"  as  a  result  of  the 
condensation  of  the  vapor  from  the  finger. 

Effect  of  vaporization  on  the  temperature 
of  the  body. — The  normal  temperature  of  the  human 


212  THIED   BOOK   OF   PHYSIOLOGY 

body  is  "between  9S  and  99  degrees  Fahrenheit.  Only 
at  this  temj^erature  can  the  body  be  said  to  be  in  a 
health}'  condition. 

The  air  is  ordinarily  cooler  than  the  blood,  and  so  heat 
is  constantly  being  radiated  from  the  body.  Frequently, 
however,  this  is  not  sufficient  to  keep  the  temperature 
down  to  normal. 

In  addition  to  radiation,  evaporation  acts  as  a  tempera- 
ture regulator.  A  liquid  cannot  evaporate  unless  it  can 
get  heat.  \Yhen  sweat  evaporates  it  can  get  the  needed 
heat  most  conveniently  from  the  body.  Thus  the  body 
is  cooled. 

The  body  automatically  regulates  its  own  temperature. 
During  a  hot  da}',  or  at  times  of  vigorous  exercise,  a 
large  amount  of  sweat  is  poured  out  on  the  surface  of 
the  skin.  Its  evaporation  cools  the  bod}'.  A  warm  wind 
feels  cool  if  the  skin  is  wet,  because  evaporation  is 
hastened.  Fanning  heats  the  air  slightly,  but  it  in- 
creases evaporation  from  the  skin,  and  so  the  air  seems 
cooler.  Fanning  a  dry  thermometer  will  not  cause  the 
mercury  to  fall. 

Heavy  clothes  keep  the  body  warm,  because  they 
check  both  the  radiation  and  the  evaporation.  Alcohol 
rubbed  on  the  skin  will  cool  the  body  more  rapidly  than 
water  will,  because  it  will  evaporate  faster. 

Hair. — Hairs,  in  more  or  less  abundance,  are  dis- 
tributed over  nearly  the  whole  surface  of  the  body. 
There  are  none  on  the  palms  or  soles.  The  root  of  a  hair 
is  the  part  beneath  the  surface  of  the  skin.    It  is  enclosed 


TIIK    SKIN 


213 


ill  ;i  follicle  or  jmcket  tbrined  by  the  involution  of  the 
epidermis,  as  shown  in  Fig.  101.     At  the  bottom  of  the 
follicle,   the  root  lits  over  ii  papilhi,  which  is   supplied 
with  blood-vessels.     Thus  the  cells 
in  the  root  of  the  hair  jire  nourished 
and  continue  to  produce  new  cells, 
which  push  the  old  ones  ahead  of 
them,  thus  increiising  the  length  of 
the  hair. 

When  a  liair  is  pulled  out,  a  new 
one  will  grow  in  its  place  if  the 
papilla  is  not  injured. 

The  outside  of  a  hair  is  covered 
with   a  single    layer   of   flat   cells 
which  overlap  like  scales.    The  free 
edge  of  the  scales  lie  tow^ards  the    fig.  1 01.— Hair-follicle. 
l^oint  of  the   hair.     B3'  rubbing  a 

hair  lengthwise  between  the  thumb  and  the  finger,  it  will 
be  moved  along  root  first. 

The  color  of  the  hair  is  determined  by  a  pigment  in 
the  cells.  In  old  age  the  coloring  matter  is  wanting, 
and  the  hair  is  white. 

Fibres  of  muscle  are  attached  to  the  hair-follicles. 
When  they  contract,  the  follicle  is  changed  from  an 
oblique  i)Osition  to  one  more  nearly  perpendicular  to  the 
surface.  Thus  the  hair  is  made  to  ''stand  on  end."  In 
some  animals,  such  as  the  cat,  frequent  use  is  made  of 
these  muscles. 

Hair  on  the  head  is  useful  for  adornment  and  for  pro- 
tection from  heat  and  cold.     The  eyelashes  andej^ebrows 


214  THIRD    BOOK    OF   PHYSIOLOGY 

protect  the  delicate  organs  of  sight.     Hairs  in  the  nos- 
trils and  ears  guard  the  entrance  to  important  organs. 

Nails. — Xails.  like  hair,  are  a  modified  form  of  epi- 
dermis. Thej'  consist  of  a  root,  hody,  and  edffc.  The 
root  is  the  back  i^art  where  the  nail  is  attached  to  the 
dermis,  and  where  there  is  a  constant  addition  of  new 
cells  which  push  the  nail  forward. 

The  body  is  the  visible  part  of  the  nail,  which  is 
attached  to  a  portion  of  the  true  skin  called  its  bed.  The 
nail  increases  in  thickness  by  the  addition  of  new  cells 
from  the  bed. 

The  nail  itself  is  quite  transjiarent.  The  color  ob- 
served is  that  of  the  true  skiu  beneath.  The  pink  color 
is  due  to  the  suj^ply  of  blood  beneath. 

The  liuuda,  or  little  moon,  near  the  root  is  of  whiter 
color  because  less  blood  flows  beneath  it,  and  it  is  less 
transparent. 

Hygiene  of  the  skin. — The  skin  is  an  exceedingly 
imi)ortant  organ  as  far  as  concerns  bodily  health  and 
comfort.  Its  chief  functions  are  protection  and  excretion. 
A  temporary  suspension  of  either  one  of  these  results  in 
sickness  or  even  death. 

The  skin,  like  any  other  organ,  can  effectively  do  its 
part  only  within  certain  limits.  For  example,  it  can, 
under  ordinary  conditions,  regulate  the  temperature  of 
the  body,  keeping  it  quite  close  to  98.5  degrees.  In  ex- 
tremes of  heat  and  cold,  however,  the  unaided  skin  is 
helx:>less  as  a  temperature  regulator. 


TllH   SKIN  215 

Clothing. — As  ill  ready  explained,  heat  is  constantly 
leaving  (lie  body  by  radiation  and  perspiration.  When 
exposed  1o  cold  weather,  perspiration  is  checked  by 
closinjif  the  i)ores,  but  radiation  becomes  more  rapid  than 
before.  For  this  reason  the  IkkIv  must  bo  piotected  with 
proper  clothing-. 

Ch)thing  does  not  warm  the  body.  It  only  prevents 
the  escape  of  heat.  In  cold  weather,  then,  a  garment 
should  be  a  poor  conductor  of  heat.  A  loose  woollen 
garment  is  good  because  much  air  is  enclosed  between 
its  loose  fibres,  and  air  is  a  very  i^oor  conductor  of  heat. 

Many  workmen  who  are  exposed  to  the  hot  sun  wear 
woollen  shirts  to  keep  the  excessive  heat  out. 

A  woollen  sweater  is  an  excellent  protection  during 
winter  and  at  all  times  when  there  is  liability  of  cooling 
off  too  suddenly. 

The  effect  of  the  color  of  clothes  is  a  matter  of  some 
importance.  Black  is  a  good  absorber  of  heat  and  also  a 
good  radiator.     White  is  poor  in  both. 

When  a  black  cloth  is  exposed  to  sunlight  or  some 
other  source  of  heat,  it  will  become  warmer  than  the 
white  cloth  ;  l)ut  when  the  source  of  heat  is  withdrawn 
the  black  will  cool  more  rapidly. 

A  black  garment  will,  on  a  cold  day,  allow  more  heat 
to  escape  from  the  body  than  a  white  one  made  of  the 
same  material. 

As  people  ordinarily  live,  white  is  the  best  color  the 
year  round,  as  far  as  the  absorption  and  radiation  of 
heat  are  concerned. 

Cotton  and  linen   goods  are  good  for   summer  wear 


216  THIRD   BOOK   OF   PHYSIOLOGY 

under  ordinary  conditions.  They  are  fairly  good  con- 
ductors of  lieat,  and  for  that  reason  the  body  will  cool 
by  radiation  if  the  surrounding  atmosphere  be  cool. 
The  greatest  advantage  of  such  goods  in  hot  weather  lies 
in  the  fact  that  they  will  readily  absorb  moisture  from 
the  skin  and  conduct  it  to  the  outside,  where  it  can 
rapidly  evaporate. 

The  kind  and  amount  of  clothing  depend  upon  the 
climate,  habits  of  life,  and  constitution  of  the  body. 
Many  of  the  ills  of  the  body  result  from  an  improper 
kind  or  quantity  of  clothing.  As  a  rule,  a  loose  woollen 
garment  next  to  the  skin  is  best  in  winter  time,  and  for 
some  it  is  best  the  year  round.  Each  one  must  suit  his 
clothing  to  his  individual  needs. 

Bathing. — Every  i)ore  of  a  healthy  body  is  con- 
stantly perspiring.  Sometimes,  as  on  exposure  to  cold, 
the  amount  of  matter  perspired  is  very  small.  At  other 
times,  when  there  is  danger  of  the  body  being  over- 
heated, a  large  amount  of  sweat  is  poured  out  on  the 
surface  of  the  body.  Along  with  the  perspired  water  is 
a  considerable  quantity  of  urea,  salts,  and  other  matter. 
When  the  water  evaporates,  these  substances  become 
dried  on  the  skin  and  clothing. 

The  oil  which  is  furnished  by  the  sebaceous  glands 
also  causes  dust  and  dirt  to  adhere  more  readily  to  the 
skin  and  hair. 

In  addition  to  this,  one  who  is  engaged  in  any  active 
occupation  must  come  in  contact  with  more  or  less  dirt 
which  clings  to  the  body. 


THE   SKIN  217 

Bathing  is  necessary  to  assist  the  skin  in  its  work  of 
excretion,  and  also  for  the  mere  purpose  of  being  clean. 

Beside  the  mere  matter  of  removing  dirt,  however,  a 
cold  bath  in  the  morning  will,  to  some  people,  be  a  stim 
ulus  to  the  whole  body  during  the  day ;  and  a  warm  bath 
just  before  retiring  will  often  induce  sound  and  restful 
sleep. 

Times  and  methods  of  bathing.— The  advice  of 
various  authorities  vary  in  regard  to  the  times  and 
methods  of  bathing.  One  may  bathe  too  often,  and  thus 
do  the  body  more  harm  than  good.  A  change  of  the 
clothing  worn  next  to  the  skin  is  often  more  essential  to 
good  health  than  the  application  of  water  and  soap. 
The  vocation  and  manner  of  life  will  help  to  determine 
how  frequently  one  should  bathe.  The  skin  may  be 
moistened  with  water  every  day  and  then  well  rubbed 
with  a  coarse  towel;  but  a  thorough  bath  everj^  week,  or 
even  every  two  weeks,  may  be  sufficient  under  ordinary 
circumstances. 

In  hot  weather  or  after  severe  exercise  baths  may  be 
more  frequent. 

The  kind  of  a  bath  is  a  matter  to  be  decided  by  each 
individual  in  accordance  with  his  state  of  health  and  his 
circumstances.     Baths  may  be  cold^  warm,  or  hot. 

The  cold  bath  may  consist  in  a  plunge  into  cold  water, 
a  cold  shower,  the  application  of  cold  water  by  means  of 
a  sponge,  or  even  dipping  the  hands  into  the  water  and 
rubbing  it  rapidly  over  the  skin. 

The  first .  effect  of  the  cold  water  is  to  close  the  pores 


218  THIPvD   BOOK   OF   PHYSIOLOGY 

and  contract  tbe  blood  capillaries  ;  but  this  should  be 
quickly  followed  by  a  reaction,  and  a  warm,  healthful 
glow  should  fee  felt  all  over  the  surface  of  the  body.  The 
body  should  be  exposed  to  the  cold  water  for  only  a  very 
short  time  and  then  vigorously  rubbed  with  a  coarse 
towel.  Unless  a  warm  glow  follows,  the  cold  bath  will  be 
injurious.  Persons  of  weak  constitution  should  be  cau- 
tious in  the  use  of  the  cold  bath  and,  if  attempted  at  all, 
it  should  be  taken  in  mild  form  at  first  until  the  body 
becomes  used  to  the  shock. 

The  warm  bath  is  the  one  commonly  used  with  soap  to 
wash  away  grease  and  dirt.  Many  people  will  never  use 
the  hot  and  cold  baths,  but  every  one  needs  the  warm  bath 
and  soap,  and  a  frequent  change  of  underclothing,  to 
keep  the  skin  in  a  healthy  condition.  Any  one  who  can 
get  a  sponge  or  wash-cloth,  some  mild  soap,  and  a  basin 
of  water,  has  no  excuse  for  not  keeping  his  body  clean. 

A  clean  skin  and  clean  clothes  improve  not  only  the 
physical,  but  also  the  moral  condition  of  the  individual. 
Hot  baths  may  be  recommended  by  physicians  in  treat- 
ment of  certain  diseases. 

Care  of  the  hair. — A  beautiful  head  of  hair  is  an 
ornament  to  its  possessor,  but  only  good  care  will  keep  it 
so.  The  hair  may  occasionally  be  washed  with  soft  water 
and  a  mild  soap,  but  only  often  enough  to  keep  it  and 
the  scalp  clean.  Massage  of  the  scalp  and  use  of  the  hair- 
brush will  stimulate  the  roots  of  the  hairs  to  healthy 
activity. 

The  natural  secretions  of   the  sebaceous  glands  will 


Tin-:  sKiK  210 

ordinarily  keep  tlic  hiiir  soft  and  <;lossy.  If  it  I>ecoiiies 
dry  iiiid  loses  its  gloss,  a  little  viiseliin'  may  be  applied 
to  it. 

A  large  mmiber  of  loose  cells  of  the  epidermis,  along 
with  oil  which  has  dried  on  the  scali),  constitutes  what 
is  called  dandruff.  Tt  indicates  a  diseased  condition  of 
the  scalp  and  is  associated  with  a  loss  of  hair. 

Care  of  nails. — (Mc^an  and  neatly-trimmed  nails  are 
a  recommendation  to  any  one.  Dirty  nails  with  jagged 
edges  indicate  careless  habits,  not  only  in  this  but  in 
other  matters.  They  should  be  cleaned  every  day  with  a 
nail-brush  and  water,  and  the  edges  should  be  occasion- 
ally trimmed  to  a  smooth  curve. 

The  epidermis  which  overlaps  the  nails  at  the  roots  and 
sides  should  be  pushed  back,  for  otherwise  it  adheres 
so  firmly  to  the  uail  that  the  skin  will  l>e  torn,  forming 
the  ^'hang-nail." 

QUESTIONS  FOR  REVIEW. 

1.  What  is  the  nature  of  the  skin? 

2.  How  does  skin  protect  the  body  ? 

3.  Why  is  the  skin  provided  with  nerves  of  touch? 

4.  Describe  the  two  layers  of  skin. 

5.  How  thick  is  the  epidermis? 

6.  What  kind  of  cells  form  the  epidermis?  How  are  they 
supplied? 

7.  Are  the  cells  of  the  epidermis  alive? 

8.  Explain  the  color  of  the  skin.     What  causes  freckles? 

9.  Describe  the  true  skin. 

10.  What  are  pores  ?    Can  you  see  them  ? 

11.  Describe  a  sweat-gland. 


220  THIRD   BOOK   OF   PHYSIOLOGY 

12.  What  is  perspiration?    Describe  two  kinds. 

18.  Try  an  experiment  to  show  insensible  perspiration. 

14.  Explain  fully  the  effect  of  evaporation  from  the  surface  of 
the  body. 

15.  Describe  the  root  of  a  hair. 

16.  What  causes  hair  to  grow? 

17.  What  causes  hair  to  stand  on  end  ? 

18.  Describe  the  nail. 

19.  How  does  a  nail  grow  ? 

20.  Explain  the  lunula. 

21.  What  is  the  use  of  clothing? 

22.  Why  will  a  woollen  garment  keep  the  body  warmer  than  a 
linen  one? 

23.  What  is  the  effect  of  the  color  of  clothing? 

24.  Why  do  cotton  and  linen  make  good  summer  garments  ? 

25.  Why  is  bathing  necessary? 

26.  How  often  should  one  bathe? 

27.  What  is  the  advantage   of  a   cold   bath  ?     When  and  how 
should  it  be  taken  ? 

28.  Why  should  clothing  worn   next  to  the  skin  be  frequently 
changed  ? 

29.  What  is  proper  care  of  the  hair? 

30.  Why  should  nails  be  kept  clean  ? 


CHAPTEK    XIV 

EXCRETION 

Secretion  and  excretion  compared.— We  have 
seeu  that  numerous  glands  are  distributed  througliont 
the  body.  All  the  gl5.nds  are  enclosures  surrounded 
with  cells,  and  opening,  as  a  rule,  by  ducts  out  onto  a 
free  surface. 

Blood  constantly  flows  through  the  numerous  capil- 
laries about  the  cells  of  the  gland,  and  from  it  is  selected 
the  various  substances,  in  accordance  with  the  i:)urpose 
of  the  gland. 

The  cells  of  a  gland  may  gather  out  liquids  which  are 
already  in  the  blood,  or  they  may  elaborate  the  materials 
which  they  collect,  and  produce  new  compounds. 

The  hydrochloric  acid  in  the  stomach,  for  example,  is 
not  taken  from  the  blood,  but  is  made  by  the  gastric 
glands. 

When  the  material  collected  by  a  gland  is  for  further 
use  in  the  body,  the  process  is  called  secretion.  For  ex- 
amples, the  saliva  and  gastric  juice  are  secretions. 

When  material  is  collected  by  a  gland  only  to  be  cast 
out  of  the  body,  the  process  is  called  excretion.  For  ex- 
ample, urea  is  excreted  by  the  kidneys  and  carbon  di- 
oxide is  excreted  by  the  lungs. 

Some  substances  are  both  secretions  and  excretions. 
For  example,  the  bile  is  an  important  agent  in  digestion, 

221 


222  THIRD   BOOK   OF   PHYSIOLOGY 

aud  so  may  be  considered  a  secretion  of  the  liver  ;  but 
bile  would  soon  make  the  blood  impure  unless  it  be  con- 
stantly eliminated  :  and  tbus  it  is  also  an  excretion. 

The  chief  excretory  organs.— The  chief  organs 
concerned  in  excretion  are  the  Jungs.  sJcin,  liver,  and 
Jtidneys. 

These  have  all  been  described  except  the  kidneys.  In 
this  chapter  we  briefly  refer  to  the  work  of  each,  aud 
describe  the  work  of  the  kidnej's  in  full. 

The  lungs. — The  lungs  are  excretory  organs  of 
very  great  importance.  We  have  already  compared 
breathing  to  a  draft  of  air  through  the  burning  fuel  of  a 
steam-engine.  In  the  engine  the  air  enters  below  the 
grate^  and  the  waste  products  of  combustion  pass  out 
through  a  chimney  above. 

In  the  body  the  air  is  supplied  to  the  blood  in  the 
lungs  and  the  i)roducts  of  combustion  are  returned  by 
the  same  channel.  Thus  the  air-passage  serves  both  for 
damper  and  chimney. 

The  chief  substance  excreted  by  the  lungs  is  carbon 
dioxide  (CO,).  This  is  the  chief  product  of  combustion 
of  coal,  wood,  coal-oil,  or  any  kind  of  carbonaceous  sub- 
stance. 

Some  organic  substances  are  also  excreted  with  every 
exhalation.  The  character  of  these  substances  is  not 
well  understood ;  but  there  is  no  doubt  of  their  presence 
in  the  breath  and  their  vitiating  effect  on  the  air  in  a 
close  room. 

Water  is  also  excreted  in  large  quantity  by  the  lungs. 


EXCRETION  223 

The  skin. — While  the  skin  is  chiefly  an  organ  for 
tlie  protection  of  the  l)0(ly,  it  also  has  an  additional 
donble  function  of  secretion  of  waste  substances  and  the 
regulation  of  bodily  temperature.  Thus  the  skin  may 
be  regarded  iis  both  secretory  and  excretory.  Its  chief 
excretions  are  water,  urea,  and  salts. 

There  is  a  close  relation  between  the  skin  and  the  kid- 
neys. When  the  excretions  of  the  skin  are  large,  the 
kidneys  are  relieved  of  much  of  their  work  ;  when  the 
glands  of  the  skin  arc  inactive,  more  work  is  thrown 
upon  the  kidneys. 

The  liver. — The  excretions  of  the  liver  depend  upon 
the  kind  of  substances  in  the  blood.  As  already  ex- 
plained, the  liver  is  a  most  efficient  guardian  of  the 
health  of  the  body.  Nothing  gets  from  the  stomach  or 
intestines  into  the  general  circulation  until  it  has  first 
been  tested  by  the  liver,  and  many  substances  that 
would  be  injurious  are  either  changed  in  their  character 
or  excreted. 

Bile  is  an  excretion  of  the  liver.  If  the  bile  should 
remain  in  the  blood,  serious  disorders  are  sure  to  follow. 
It  is  made  to  serve  a  useful  purpose  in  intestinal  diges- 
tion, and  much  of  it  may  again  enter  the  portal  veins 
and  be  again  excreted,  or  secreted,  by  the  liver. 

Kidneys. — The  kidneys  are  among  the  most  impor- 
tant of  the  excretory  organs.  A  man  could  not  live 
more  than  one  day  if  the  action  of  his  kidneys  would 
cease. 


224 


THIED   BOOK   OF   PHYSIOLOGY 


They  are  two  in  number  and  are  located  in  the  abdo- 
men, one  on  each  side  of  the  spinal  column,  in  the  region 
of  the  loins. 

Each  is  about  four  inches  long,  two  inches  broad,  and 
one  inch  thick.     They  are  shaped  somewhat  like  a  beau, 


Fig.  102.  —  Cross-section  of  kidney.  C,  C.  cortex:  M,  pyramids 
of  Miilpighi ;  L.  L,  medulla;  P,  pelvis;  .4,  artery;  T,  vein;  U, 
ureter. 

and  on  the  side  towards  the  backbone  is  a  depression 
called  the  hihnn.  Three  tubes  enter  the  kidney  at  the 
hilum.  One  is  the  renal  artery,  which  carries  blood  to 
the  kidney  ;  another  is  the  renal  vein,  which  carries  the 


EX(MM^TI()X  225 

blood  away  ;  and  between  them  is  the  ureter,  wliich  ear- 
ries  the  excretions  of  the  kidney  to  the  bhidder. 

Internal  structure  of  the  kidney.  -A  longitu- 
dinal section  of  a  kidney  would  lia\e  ab(jut  th(*  appear- 
ance shown   in  Fig.   102.     The  ureter  on  entering   the 


Fig.  108. — Section  of  cortex  of  a  kidney,  showing  Malpighian  bodies 

slightly  magnified. 

kidney  spreads  out,  forming  a  cavity  called  the  pelvis  of 
the  kidney.  Projecting  into  the  pelvis  are  a  number  of 
pyramids,  from  eight  to  eighteen  in  number,  and  known 
2iS>i\\Q  pyramids  of  Malpiglu.  The  pyramids  project  from 
the  medullary  layer  of  the  kidney.  Surrounding  the  med- 
io 


226 


THIRD   BOOK   OF   PHYSIOLOGY 


ullary  layer  is  the  cortex.     The  kidneys  are  enclosed  and 
held  in  place  by  a  capsule  of  fatty  areolar  tissue. 


Microscopic  examination  of  the  kidneys. — 
Minute  examination  of  the  cortex  shows  that  it  contains 
numerous  spherical  bodies  about  y^^  of  an  inch  in  diam- 
eter. These  are  known  as  the  ^lalpighian  bodies.  It  is  in 
these  that  the  excretion  of  the  kidney  is  chiefly  done. 

Each  little  sphere  is  composed 
of  two  parts,  as  shown  in  Fig, 
104.  ^\"ithin  is  a  roll,  or  tuft, 
of  capillary  blood-vessels,  to 
which  blood  is  supplied  by 
an  artery  called  the  afferent 
vpssel.  Leading  out  of  the 
tuft  is  an  artery  called  the 
efferent  vessel.  This  again 
breaks  into  capillaries  around 
the  convoluted  tubule,  and 
these  are  gathered  into  ceins. 
The  tuft  of  capillaries  is  en- 
closed in  a  capsule  from  which 
a  tube,  called  the  uriniferoiui 
tubule^  carries  the  excretions  to 
the  pelvis  of  the  kidney. 

The  uriniferous  tubules  be- 
gin at  the  Malpighian  bodies 
in   the   cortex   and   pursue  a 
circuitous  route  through  the  cortex  and  the  medullary 
layer  to  straight  collecting  tubes  which  open  at  the  apex 


Fig.  10-1. —  Showing  struc- 
ture of  Malpighian  body  and 
uriniferous  tubule.  J,  artery; 
4/".  afferent  vessel;  3/,  Mal- 
pighian body  ;  T,  tuft  of  blood 
capillaries  ;  V,  uriniferous  tu- 
bule ;  Ef.  efferent  vessel;  ]'. 
vein.  The  blood  first  passes 
through  the  capillaries  of  the 
^lalpighian  body  and  then 
through  the  capillaries  about 
the  uriniferous  tubule. 


EXCEETTOX 


227 


of  the  pyramids  into  the  pelvis  of  the  kidney.  Fv^.  105 
is  a  liijj^hly  inajj^nificd  section  of  kidney,  showing  some 
branchfs  of  a  collecting  tube.  All  the  secretions  are 
thus  brought  to  the  pelvis  and  drained  off  by  the  ureter. 


^' ? 


Fig.  105. — Section  of  cortex  of  kidney,  hiijhly  magnified,  show- 
ing Malpighiaii  bodies  and  the  tubes  leading  to  the  pelvis  of  the 
kidney. 


The  excretions  of  the  kidney.— The  substances 
excreted  by  the  kidneys  are  urea,  salts,  other  waste,  and 
a  large  quantity  of  water.  The  amount  of  liquid  excreted 
in  one  day  is  about  three  pints,  about  one  ounce  of 
which  is  urea. 

The  chief  function  of  the  kidneys  is  to  excrete  urea. 
The  water  is  necessary  that  the  other  substances  may  be 
in  solution  and  thus  be  carried  along. 

The  chief  excretion  of  the  Malpighian  bodies  is  water. 


228  THIED   BOOK   OF   PHYSIOLOGY 

The  urea  is  excreted  by  the  cells  which  line  the  urinifer- 
ous  tubules. 

Urea  is  the  product  resulting  from  the  use  of  proteid 
food.  In  the  chapter  on  food  it  was  shown  that  proteid 
is  the  only  food  which  contains  nitrogen.  Urea  also  con- 
tains nitrogen.  The  chemical  symbol  for  urea  is  COX,H^. 
Urea  is  gathered  from  the  blood  current  by  the  liver,  and 
then  the  kidneys,  with  a  little  help  from  the  skin,  excrete 
this  waste  product  of  the  proteids.  When  the  amount 
of  nitrogen  excreted  is  equal  to  the  amount  of  nitrogen 
in  the  i)roteid  food,  there  is  said  to  be  nitrogenous  equilib- 
rium. In  this  case  the  muscles  neither  gain  nor  lose  in 
weight.  In  case  of  starvation  the  urea  continues  to  be 
excreted,  but  it  results  from  the  fact  that  the  muscles 
themselves  are  being  used  as  proteid  food.  Thus  the 
muscles  waste  away  and  the  body  loses  in  weight. 

Diseases  of  the  kidneys.— When  the  kidneys  are 
removed  from  an  animal,  death  speedily  ensues.  The 
urea  accumulates  in  the  blood  and  produces  blood-poison- 
ing. 

Even  a  partial  and  temporary  suspension  of  the  work 
of  the  kidneys  always  results  seriously  to  the  welfare  of 
the  whole  body. 

Colds  often  cause  an  affection  of  the  kidneys  by  causing 
the  skin  to  suspend  its  work  as  an  excretory  organ. 
Extra  work  is  thus  thrown  upon  the  kidneys,  and,  if  it  is 
overworked,  a  diseased  condition  is  produced. 

Alcoholic  drinks  injure  the  kidneys  more,  probably, 
than  any  other  known  cause. 


EXrHF/nON  229 

The  cells  of  the  tubules  and  Malpighian  bodies  become 
changed,  so  that  thoy  no  lonjjer  perform  well  their 
natural  functions.  Albumen  of  the  blood  is  then  often 
allowed  to  pass  out  of  the  cai)illaries  with  the  other 
secretions.  This  condition  is  known  as  Bright' s  disease. 
Eminent  physicians  say  that  alcoholic  drinks  are  one 
cause  of  this  fatal  disease. 

Fatty  degeneration  of  the  kidneys  is  another  result  of 
using  alcoholic  drinks.  '  Parts  of  the  tissue  of  the  kidney 
are  replaced  by  fat.  Thus  the  secreting  organ  is  in  fact 
decreased  in  size,  for  the  fat  can  have  no  part  in  the 
work  of  excretion.  Extra  work  is  thus  thrown  upon  the 
remaining  parts  of  the  kidneys,  or  the  blood  is  allowed 
to  pass  on  through  without  proj^er  purification,  and  the 
whole  body  suffei's  the  consequence. 

Alcohol  also,  as  already  explained,  interferes  with  di- 
gestion and  the  excretions  of  the  liver.  Thus  injurious 
substances  are  introduced  into  the  circuit  of  the  blood. 
The  kidney  attempts  to  eliminate  these  in  addition  to  its 
natural  work.  As  a  result  the  kidney  is  overtaxed  and 
becomes  inflamed  and  diseased. 

Over-eating,  also,  or  the  eating  of  rich  and  highly-sea- 
soned food,  is  the  cause  of  much  kidney  trouble. 

All  parts  of  the  body  sutfer  from  any  affection  of  the 
kidneys  because  the  purity  of  the  blood  is  at  once  im- 
paired. 

QUESTIONS   FOR   REVIEW. 

1.  What  is  the  source  of  the  hydrochloric  acid  in  the  stomach? 

2.  What  is  secretion?    Give  examples. 

3.  What  is  excretion?    Give  examples. 


230  THIRD    BOOK    OF    PHYSIOLOGT 

4.  Is  bile  a  secretion  or  an  excretion? 

5.  Xame  the  chief  excretory  organs. 

6.  Describe  the  excretions  of  the  lungs. 

7.  Do  the  air-passages  correspond  to  the  damper  or  the  chimney 
of  a  stove  ? 

8.  How  can  you  show  that  there  is  water  in  tlie  breath? 

9.  What  does  the  skin  excrete? 

10.  Is  the  water  in  sweat  an  excretion  or  a  secretion  ? 
.    11.  For  what  two  purposes  is  bile  produced  by  the  liver? 

12.  Locate  and  describe  the  kidneys. 

13.  !Make  a  drawing  of  a  section  of  a  kidney,  showing  cortex, 
medullary  layer,  pyramids,  pelvis,  ureter,  and  blood-vessels. 

14.  Describe  a  Malpighian  body. 

15.  Describe  a  uriniferous  tubule. 

16.  What  is  excreted  by  the  kidneys? 

17.  What  is  the  cause  of  urea  in  the  blood? 

18.  Explain  "nitrogenous  equilibrium." 

19.  Why  does  one  lose  flesh  during  sickness? 

20.  How  important  is  the  work  of  the  kidneys? 

21.  How  does  a  cold  affect  the  kidneys? 

22.  What  is  Bright' s  disease?    What  may  cause  it ? 

23.  Explain  "fatty  degeneration"  of  the  kidneys. 

24.  In  what  other  ways  does  alcohol  have  a  bad  effect  on  the 
kidneys  ? 

25.  Why  does  the  whole  body  suffer  when  the  kidneys  do  not 
act? 


CHAPTER     XV 

THE   NERVOUS  SYSTEM 

The  need  of  a  controlling  organ. — A  number  of 
dift'erent  systems  and  organs  have  already  l>een  explained. 
Some  are  concerned  in  the  movements  of  the  body.  Some 
take  in  and  digest  the  food.  Some  distribute  food  and 
oxvgren  to  the  cells.  Others  rid  the  bodv  of  waste  and 
impurities,  and  numerous  others  still  are  at  work  in  one 
way  or  another  for  the  welfare  of  the  whole  body. 

Each  organ  must  work  in  liarmony  with  all  the  others, 
or  it  itself  must  soon  sutler.  For  example,  the  tissues  of 
the  hands  and  arms  need  food  :  but.  although  the  hands 
be  loaded  with  the  best  kind  of  food,  the  tissues  cannot 
get  it  until  it  is  properly  prepared  by  several  other 
organs.  The  hand  carries  the  food  t<»  the  mouth  :  there 
it  is  masticated  and  mixed  with  saliva  :  then  it  is  swal- 
lowed, and  digested  in  the  stomach  and  intestines  :  thence 
it  passes  over  into  the  current  of  blood,  and  is  distrib- 
uted to  the  cells  of  the  body.  Thus  the  hands,  by  which 
the  first  act  of  this  process  was  accomplished,  are  de- 
pendent on  the  organs  of  digestion,  and  the  organs  of 
digestion  depend  on  the  hands  to  bring  food  within  their 
reach. 

In  a  similar  way  each  organ  must  rely  upon  the  co- 
operation of  the  othei^,  and  the  failure  of  any  one  im- 
portant organ  will  result  in  the  destruction  of  all. 

231 


232  THIPvD    BOOK    OF    PHYSIOLOGY 

Froui  this  it  is  plain  that  there  must  be  one  organ,  or  a 
collection  of  them,  which  shall  have  a  controlling  and  di- 
recting influence  uj^on  the  others,  and  which  shall  not 
only  cause  all  i^arts  to  work  in  harmony,  but  also  iji  pro- 
portion to  the  demands  of  the  body  at  different  times. 

This  important  function  is  performed  by  the  nervous 
system. 

An  organized  body  of  men. — The  human  body 
may  be  considered  as  a  number  of  units,  each  with  a  dif- 
ferent function  and  all  working  together  as  an  organized 
body.  The  relation  of  these  various  units  may  be  made 
clearer  by  a  comparison  with  a  number  of  men  who  bind 
themselves  together  in  an  organized  body  for  the  accom- 
plishment of  a  definite  purpose.  In  such  an  organization 
a  variety  of  different  kinds  of  work  must  be  done,  and 
each  man  selects  the  kind  which  he  can  do  best  and  does 
that  only.  Each  member  knows  that  his  success  depends 
on  the  success  of  the  whole  organization,  but  however 
o'ood  his  individual  work  mav  be.  his  efforts  mav  not  be 
effective  unless  there  is  some  way  to  direct  his  work  in 
accordance  with  what  is  being  done  by  the  other  mem- 
bers. So,  in  such  an  organization,  a  president  is  always 
selected,  and  it  is  his  business  to  so  direct  the  work  of 
each  that  the  general  results  may  be  most  effective. 

Heads  of  departments  may  also  be  appointed,  and  they 
may  look  after  many  matters  of  detail  without  reporting 
them  to  the  iDresident.  Each  man  may  after  a  time  be- 
come so  expert  in  his  work  that  he  can  be  trusted  to 
continue  it  without  constant  direction. 


THE    XKHVorS    SYSTI':>r  233 

Wlienever  one  menihei-  of  the  organization  fails  to  do 
liis  j)art  or  fails  to  work  in  harmony  with  the  others, 
then  the  president  must  be  notified  and  the  matter 
adjusted,  or  the  organization  will  break  down. 

All  the  relations  just  pointed  out  between  the  presi- 
dent and  the  other  members  of  the  organization  are 
similar  to  those  between  the  nervous  system  and  the 
other  organs  of  the  body. 

The  nervous  system. — Tlie  nervom  system  is  com- 
posed of  nerve-centres,  nerves,  and  special  organs  at  the 
ends  of  nerves.  The  nerve-centres  are  the  brain,  the  spinal 
card,  and  ganglia.  The  nerves  all  originate  in  the  nerve- 
centres  and  extend  out  to  the  parts  to  which  impulses 
are  to  be  sent  or  from  which  impulses  are  to  be  received. 

There  is  but  one  great  nervous  system,  with  centres 
here  and  there,  and  nerve-trunks  and  nerve-fibres  rami- 
fying to  every  part  of  the  body,  the  whole  system  being 
more  or  less  intimately  joined  together.  But,  because 
of  certain  differences  in  character  and  function,  the 
system  is  divided  into  two  parts.  The  first  is  called  the 
cerebrospinal  or  central  nervous  system,  and  includes  the 
brain,  the  spinal  cord,  and  the  nerves  leading  out  from 
them. 

The  second  is  called  the  Sympathetic,  or  Ganglionic, 
nervous  system,  and  includes  numerous  small  nerve-centres 
called  ganglia,  and  the  nerves  which  issue  from  them. 
The  sympathetic  system  is  chiefly  concerned  with  the 
involuntary  movements  of  the  body,  such  as  those  in- 
volved in  digestion,  circulation,  and  respiration. 


23; 


THIRD   BOOK   OF   PHYSIOLOGY 


The  nerve-cell.— Nerve-cells,  like  other  cells,  are 
composed  of  minute  masses  of  protoplasm  containing  a 
nucleus  and  a  nucleolus.  A  very  noticeable  character- 
istic of  a  nerve-cell  is  its  tending  to  send  off  many  pro- 
cesses from  the  cell-body.  Part  of  the  processes  are 
short,    and    soon   divide   into   numerous    fine  branches 


Fig.  106. — Xeurons  from  the  gray  matter  of  the  cerebrum.  Cell- 
body,  dendrites,  and  short  portion  of  the  axis-cylinder  are  shown.  A 
micro  photocrraph. 

within  the  gray  matter  of  the  nerve-centres.  These 
branches  are  called  dendrites  because  thej^  resemble,  in 
form,  the  branches  of  a  tree. 

One  process  of  the  cell,  usually  much  longer  than  the 
others,  is  called  the  axis-cylinder.  It  may  extend  out  as 
far  as  two  or  three  feet  from  the  bo(h'  of  the  cell.  The 
axis-cylinder  is  a  fine  thread  of  protoplasm  continuous 


TllK    NERVOUS   SYSTEM  235 

with  the  cell  material.  The  cell-body,  the  dendrites, 
and  the  axis-cylinder  with  its  sheath  and  special  endings 
all  constitute  one  cell.  This  cell  is  as  much  alive  as  any 
of  the  one-celled  animals  described  in  the  fii-st  chapter 
of  this  book.  The  processes  of  nerve  cells  do  not  have 
movement  as  in  the  case  of  the  amoeba ;  but  if  the  axis- 
cylinder  of  a  nerve-cell  be  severed,  that  part  of  it  which 
is  thus  deprived  of  connection  with  the  cell-body  and 
the  nucleus  will  deteriorate  and  pass  away. 

The  unusual  extension  of  a  fine  thread  of  the  cell 
material  is  the  one  thing  about  a  nerve-cell  which  makes 
it  so  different  from  the  other  cells,  and  also  makes  it 
possible  for  nervous  matter  to  exercise  a  controlling  and 
directing  influence  over  other  cells. 

The  unit  of  the  nervous  system,  the  neuron. — 
Such  a  cell  as  we  have  just  described  is  called  a  neuron. 
The  neuron  is  the  unit  of  the  nervous  system.  The 
whole  nervous  system  is  a  collection  of  a  vast  numl)er  of 
these  units. 

Since  the  axis-cylinder  is  a  very  delicate  thread  of 
protoplasm,  it  is  protected  by  one  or  more  membranes 
which  surround  it.  Xearly  all  the  axis-cylinders  of  the 
cells  in  the  central  nervous  system  have  two  coverings, 
as  shown  in  Figs.  107  and  108.  The  first,  called  the  medul- 
lary sheath,  lies  next  to  the  axis-cylinder  and  consists  of 
a  white,  oily  substance.  It  is  this  sheath  which  gives  to 
many  nerves  their  pure  white  apjjearance.  Outside  of 
this  is  a  thin  ehistic  sheath  called  the  neurilemma. 

The  medullary  sheath  is  broken  at  intervals  of  about 


236 


THIRD   BOOK   OF   PHYSIOLOGY 


Fig.  107.— Diagram  of  a  neuron,  c,  body 
of  cell ;  ?i,  nucleus  ;  t^  dendrites  ;  a,  axis- 
cylinder ;  w,  medullary  sheath  (the  white 
matter)  ;  «,  neurilemma;  L  nucleus  of  the 
neurilemma ;  f/,  nodes  ;  e,  endings. 


Fig.  108.  —  A  medullated 
nerve-fibre,  treated  with  osmic 
acid,  and  highly  magnified.  1, 
its  nucleus;  2,  node;  3,  the 
axis-cj-linder ;  4,  membranous 
sheath  of  the  internode ;  5, 
medullary  sheath  (the  thick 
black  line). 


TITE    NKRVOrS    SYSTIOM 


237 


J^  of  :iii  iiicli  1)\'  mxlrs.  Tlu;  iiciirilciiniKi  is  c.ontiniKHis 
throuj^huut  the  whole  hMi«;lh  of  Ihr  nerve-libic,  and  in 
it  ;ue  (Miibedded  nnclei,  one  in  cucli  intcrnode. 

Fibres  which  are  covered  )>y  bolii  tliese  sheaths  sire 
called  mnhdlated  nerve -fibres,  and  sncli  an-  always  white. 

Other  fibres,  chielly  those  of  th<'  sympathetic  nervous 
system,  have  no  medullary  sheath,  and  so  are  gray  in 
color.     These  are  called  non-medullaled  nerve  fibres. 

Nervous  tissue. — Nerve  tissue  is  composed  of  gray 
and  white  matter.     The  gray  is  the  essential  part  of  the 


Fig.  109. — Neuroglia  cells. 

system  and  is  composed  of  the  protoplasm  of  the  cell 
bodies  and  the  axis-cylinder.  Wherever  a  number  of 
cells  are  clustered  together,  the  matter  is  gray,  as  in  the 
brain,  the  spinal  cord,  and  the  ganglia. 


238  THIRD    BOOK    OF    PHYSIOLOGY 

The  white  matter  is  composed  of  nerve-fibres,  the 
whiteness  being  due  to  the  medullary  sheath  around  the 
axis- cylinder. 

Both  the  gray  and  the  white  matter  are  supported  and 
held  together  by  the  ordinary  connective  tissue,  and  also 
by  another  tissue  called  neurogJia.  Xeuroglia  is  peculiar 
to  the  nervous  system.  A  few  of  its  cells  are  represented 
in  Fig.  109. 

The  brain. — The  brain  is  the  large  nerve-centre  of 
the  body.  It  is  enclosed  within  the  bony  walls  of  the 
cranium  and  is  surrounded  by  three  membranes.  The 
outer  membrane  is  called  the  dura  mater.  It  lies  next 
to  the  inner  surface  of  the  skull.  The  inner  mem- 
brane, called  the  pia  mater,  adheres  closely  to  the  sur- 
face of  the  brain,  passing  in  and  out  through  all  of  its 
folds. 

Between  the  two  is  the  arachnoid  (like  a  spiders  web), 
so  called  because  it  is  transparent  and  very  thin.  It  is 
transparent,  however,  only  in  the  sense  that  lace  or  a 
spiders  web  is  transparent.  It  invests  the  whole  sur- 
face of  the  brain,  but  does  not  follow  the  pia  mater  into 
the  folds.  Spaces  between  the  arachnoid  and  the  pia 
mater  are  filled  with  cerebrospinal  fluid.  This  fluid  is 
nearly  pure  water,  and  its  purpose  seems  to  be  to  protect 
the  brain  in  case  of  sudden  jars  or  concussions. 

The  pia  mater  is  a  very  vascular  membrane. — that  is, 
it  contains  numerous  blood-vessels  for  the  supply  of 
nourishment  to  the  brain. 

The  three  membranes  are  together  called  the  meninges, 


TUK    XKIJVors   SYSTEM 


239 


and  wlu'u  tliey  Ixicoine  iiiMamo<l  the  disease  is  known  as 
cen'brospimd  mrningitis. 

The  human  brain  is  lai<;er,  in  i)roi)ortion  to  the  size 
of  the  body,  than  tliat  of  any  other  animal.  Its  ayeraj'e 
weigcht  is  a  little  more  than  three  pounds.  The  wei^rht 
of  the  brain  of  Cuyier,  the  French  naturalist,  was  (JG 
ounces;  that  of  Webster,  the  American  orator,  G.'!!- 
ounces  ;  of  Byron,  the  English  poet,  64  ounces  ;  of  Gauss, 
the  mathematician,  53 -ounces.  The  brains  of  some  in- 
telligent men  are  less  than  the  ayerage  in  weigiit,  and 
those  of  some  idiots  much  heavier. 

Divisions  of  the  brain.— The  brain  is  divided  into 
several  parts  which  diifer  in  function  and  composition. 


Fig.  110. — The  brain  as  seen  from  the  right  side. 

The  most  important  parts  are  the  cerebrum,  the  cerebellum^ 
the  pons,  and  the  medulla  oblongata.  The  cerebrum  is  the 
most  essential  part  of  the  human  brain,  and  is  so  called 


240 


THIRD    BOOK    OF   PHYSIOLOGY 


from  the  Latin  word  cerebrum,  wbicli  means  brain.  Cere- 
bellum is  the  diminutive  of  cerebrum  and  means  little 
brain.  Pons  is  a  Latin  word  meaning  bridr/e.  Medulla 
means  marroiv. 

The  cerebrum. — The  cerebrum  occupies  the  whole 
upper  portion  of  the  cavity  of  the  cranium.     It  is  the 


Fig.  111. — Top  of  cerebrum  showing  median  fissure  and  convolution.s. 

brain  j)i"oper,  the  other  parts  being  more  or  less  only 
aids.  By  weight  the  cerebrum  constitutes  about  two- 
thirds  of  the  whole  brain. 

A  median  fissure,  extending  from  front  to  back,  di- 
vides the  cerebrum  into  the  7'igJit  and  left  hemispheres. 
(Fig.  111.)  The  two  hemispheres  are  connected  by  a 
broad  band  of  nerve- fibres  called  the  corpus  callosum,, 
shown  in  Fig.  112. 

Other  fissures,  irregular  in  outline  and  not  so  deep  as 


TTIR   NERVOUS   SYSTEM 


241 


the  median,  divide  the  liemisplieies  into  lobes,  which  are 
given  names  in  accordance  with  the  names  of  the  l>ones 
of  the  skull  beneatli  wliicli  thej'  lie. 

Thus  there  are  the  frontal,  the  panetaJ,  the  temporal, 
and  the  oecipital  h)l)es. 

The  whole  surface  of  the  cerebrum  is  covered    witli 


Fig.  112. — Cross-secdon  of  brain.     Left  half. 


gray  matter  to  a  depth  of  from  one-sixth  to  one-twelfth 
of  an  inch.     It  is  called  the  cortex  of  the  cerebrum. 

This  matter  is  composed  of  the  cell-bodies,  their  sup- 
porting tissue,  and  the  blood-vessels  concerned  in  their 
nutrition.  Beneath  the  gray  is  the  white  matter,  which 
is  composed  of  the  medullated  nerve-fibres  leading  from 
or  to  the  cells. 

On  the  surface  of  the  cerebrum  are  numerous  deep 
convolutions  or  folds,  which  afford  a  large  surface  for 
the  gray  matter.     The  number  and  depth  of  the  convo- 

16 


242 


TIIIED   BOOK   OF   PHYSIOLOGY 


lutions  are  the  chief  distinguishing  marks  between  the 
brain  of  man  and  tliat  of  the  lower  animals,  and  also  be- 
tween that  of  the  liigher  and  lower  races  of  men. 


Fig.  113. — A  portion  of  a  horizontal  section  of  a  cerebral  hemisphere, 
showing  convolutions. 

The  cerebellum.— The  cerebellum— the  lesser  brain 
— constitutes  about  one-eighth  of  the  whole  brain,  and  so 
is  called  the  lesser  brain.  It  lies  beneath  the  posterior 
part  of  the  cerebrum,  as  shown  in  Fig.  110.  It  is  com- 
posed of  gray  and  white  matter,  the  gray  being  arranged 
in  parallel  ridges. 

A  cross-section  of  the  cerebellum  shows  that  the  white 
matter  enters  each  of  its  hemispheres  as  a  trunk,  and  by 
numerous  branches  is  distributed  to  all  parts  of  the  sur- 
face. (Fig.  112.)  From  this  api^earance  the  cerebellum 
has  been  called  the  tree  of  life. 


The  pons. — The   pons   is  situated   below   the   cere- 
brum and  in  front  of  the  cerebellum.     It  is  composed 


TIIK    NKIiVOUS   SVSTKM  243 

of  both  gray  and  white  matter',  and  is  ;il)()ut  one  inch 
long  and  a  littk^  more  in  thickness.  Nerves  from  the 
spinal  cord  pass  up  througli  it  lo  tlic  cerebrum  and 
cerebellum,  and  transverse  libres  i)avSs  through  it  from 
one  side  of  the  cerebellum  to  the  other.  Thus  the  pons 
serves  as  a  bridge  by  moans  of  which  communication 
can  be  made  from  one  part  of  the  nervous  system  to 
another. 

The  medulia  oblongata. — The  medulla  oblongata 
is  that  i)art  of  the  upper  end  of  the  spinal  cord  enclosed 
within  the  skull.  It  is  about  one  and  a  quarter  inches 
in  length  and  about  one  inch  through  its  thickest  part. 
A  fissure  on  both  its  anterior  and  posterior  sides  divides 
it  into  two  equal  parts.  Both  the  gray  and  the  white 
matter  are  found  in  the  medulla,  the  gray  being  col- 
lected into  groups  which  are  more  or  less  independent 
of  each  other,  and  which  are  the  origin  of  some  of  the 
most  important  nerves. 

Nearly  all  the  fibres  of  the  spinal  cord  cross  over,  in 
the  medulla,  to  the  other  side,  and,  continuing  on  their 
way,  make  connection  with  the  cerebrum  and  cerebel- 
lum. Thus  the  nerves  from  the  right  hemispheres  of  the 
brain  are  distributed  to  the  left  side  of  the  body,  and 
those  from  the  left  hemispheres  to  the  right  side. 

Nerves. — The  neuron  has  already  been  described. 
The  axis-cylinder  with  its  i>rotecting  sheaths  is  a  nerve- 
fibre.  A  nerve  is  simply  a  number  of  nerve-fibres  run- 
ning side   by   side   and  bound   together  by  connective 


244 


THIRD   BOOK   OF   PHYSIOLOGY 


tissue,  in  wliicli  are  blood-vessels  that  coiivej^  uourish- 
ment  to  the  nerve  tissue. 

Around  the  whole  bundle  of  fibres  is  another  sheath 
called  the  perineurium. 

The  nerve-fibres  lie  close  together  in  a  nerve,  but  each 
is  independent  of  the  others  throughout  its  whole  course. 


Fig.  114. — Portion  of  a  cross-section  of  a  nerve  showing  the  ends  of 
nerve-fibres.      A  niicrophotograph. 

Whatever  communication  there  is  from  one  fibre  to  an- 
other, it  does  not  appear  to  be  along  any  kind  of  connect- 
ing fibre. 

I^erves  are  smooth,  white,  shining  cords  which  vary 
in  size  from  those  scarcely  visible  by  the  naked  eye  to 
the  great  sciatic  nerve,  which  is  about  one-half  inch 
wide  and  one-sixth  inch  thick,  and  extends  from  the 
lower  end  of  the  spinal  cord  down  to  the  toes,  sending 
off  some  fibres  along  its  whole  course,  and  growing  less 
and  less  in  size  as  it  descends. 

A  nerve  may  be  compared  to  a  cable  such  as  is  used  in 
a  telephone  system,  where  several  hundred  copper  wire3 


TUK    XI^RVOrS    SYSTK.U  245 

are  encased  in  a  lead  tube.  Each  wire  corresponds  to 
the  axis-cylinder  of  a  nerve-fibre.  Around  each  wire  is 
a  loose  wrapping  of  paper,  corresponding  to  the  sheaths 
about  the  axis-cylinder.  Around  the  whole  bundle  of 
wires  is  the  lead  tube,  which  corresponds  to  the  peri- 
neurium of  the  nerve. 

The  copper  wires  serve  only  as  conductoi'S  along 
which  electricity  may  flow  from  a  battery  or  other 
source  of  electricitj^  to  a  machine  or  device  which  it 
operates  at  the  other  end. 

Xerve-fibres,  also,  are  only  paths  along  which  impulses 
travel  from  a  nerve-centre  to  the  part  of  the  body  which 
they  stimulate.  There  is  this  difference,  however,  be- 
tween an  electric  current  passing  over  a  wire  and  an 
impulse  passing  over  a  nerve, — the  whole  of  the  energy 
which  operates  a  telegraph,  telephone,  or  motor  passes 
over  the  wire,  while  in  a  nerve  only  enough  energy 
passes  to  stimulate  to  activity  the  i^otential  energy 
already  stored  in  the  parts  to  which  the  nerves  are 
distributed. 

The  illustration  is  more  nearly  true  in  the  case  where, 
by  pressure  of  an  electric  button,  a  slight  current  of 
electricity  is  made  to  operate  a  device  which  opens  a 
valve  and  admits  steam  to  the  engines,  which  in  turn 
operate  the  machinery  of  a  factory  or  exposition. 

Efferent  and  afferent  nerves. — All  nerve  fibres 
appear  to  be  alike  in  structure,  but  experiment  shows 
that  there  are  two  kinds,  at  least  as  far  as  their  functions 
are  concerned.      One  kind  conducts  impulses  out  from 


246  THIRD   BOOK   OF   PHYSIOLOGY 

nerve- centres,  and  so  are  called  efferent  or  motor  fibres. 
Another  kind  conducts  impulses  towards  the  nerve- 
centres  and  are  called  afferent  or  sensory  nerve-fibres. 

Efferent  or  motor  impulses  stimulate  the  muscles, 
glands,  or  other  parts  of  the  body  to  activity. 

Afferent  or  sensory  impulses  keep  the  nerve-centres 
informed  in  regard  to  the  condition  of  the  body  and  its 
relation  to  other  objects. 

The  cranial  nerves. — Twelve  pairs  of  nerves 
arise  in  the  brain  and  pass  out  through  openings  in  the 
cranium  to  the  eyes,  the  ears,  the  mouth,  the  nose,  and 
other  important  organs  of  the  body.  They  are  called 
cranial  nerves. 

The  first  are  the  nerves  of  the  sense  of  smell.  They 
are  called  olfactory  nerves,  and  run  from  the  nostrils  to 
the  base  of  the  cerebrum. 

The  second  are  the  optic  nerves,  or  nerves  of  sight. 
They  extend  from  the  eyeballs  to  the  base  of  the  cere- 
brum. Both  the  first  and  the  second  pairs  are  purely 
sensory. 

The  third,  fourth,  and  sixth  i)airs  are  motor  nerves 
whieli  run  to  the  muscles  that  move  the  eyeballs. 

The  fifth  pair  are  both  motor  and  sensory,  and  are 
distributed  to  various  portions  of  the  face. 

The  seventh  pair  are  distributed  to  the  muscles  of  the 
face  and  scali).  They  arise  from  the  medulla  oblongata, 
as  do  all  the  nerves  of  the  last  six  pairs. 

The  eighth  are  the  auditory  nerves,  or  nerves  of  hear- 
ing.    They  are  purely  sensory. 


TJIE   NERVOUS   SYSTEM  247 

The  ninth  are  the  gustatonj  nerves,  or  nerves  of  taste, 
and  also  the  motor  nerves  of  the  i^harynx. 

The  tenth  i)air  extends  farther  from  the  brain  than 
any  other  of  the  twelve  pairs.  They  are  called  the 
pneumogastric  nerves  because  of  their  important  functions 
in  relation  to  the  lungs  and  stomach.  They  are  also 
called  the  vagi,  or  wandering  nerves,  because  they  are 
distributed  to  so  many  organs.  Branches  of  these  im- 
portant nerves  are  distributed  directly  to  the  pharynx, 
the  oesophagus,  and  stomach,  the  larynx,  trachea,  and 
lungs,  and  indirectly,  through  the  sympathetic  nerves, 
to  the  heart,  liver,  pancreas,  spleen,  kidneys,  small  intes- 
tines, and  large  blood-vessels. 

The  eleventh  pair  are  distributed  to  the  muscles  of  the 
neck,  and  the  twelfth  pair  to  the  muscles  of  the  tongue. 
Nerve-fibres  from  the  cells  of  the  brain  are  distributed 
not  ouh'  to  the  other  parts  of  the  body,  but  connection 
is  made  from  one  hemisphere  of  the  cerebrum  to  the 
other  by  numerous  fibres  through  the  corpus  callosum, 
and  numerous  other  fibres  connect  the  lobes  and  con- 
volutions of  the  cerebrum  with  each  other. 

The  spinal  cord. — The  spinal  cord  is  a  bundle  of 
nerve-fibres  enclosing  an  axis  of  gray  matter  composed 
of  nerve-cells.  It  is  about  eighteen  inches  long  in  the 
adult,  and  extends  from  the  large  opening,  the  foramen 
magnum  in  the  occipital  bone,  down  to  the  lower  part  of 
the  body  of  the  firet  lumbar  vertebra. 

The  spinal  foramina  of  the  vertebrae  form  the  spinal 
canal  within  which  the  spinal  cord  lies. 


248 


THIRD   BOOK   OF   PHYSIOLOGY 


The  cord  is  surrounded  by  three  membranes,  the  dura 
mater,  the  arachnoid,  and  the  pia  mater,  all  of  which  are 
continuations  of  membranes  of  the  same  names,  already 
described  as  coverings  of  the  brain. 


y'f^^ 


:  -Wi^ 


Fig.  115. — Ding-ram  of  cross-section  of  spinal  cord.  A,  anterior 
fissure  ;  P,  posterior  fissure  ;  G,  gray  matter  ;  W,  white  matter.  The 
small  circle  at  the  centre  is  a  cross-section  of  a  minute  canal  which 
runs  the  whole  length  of  the  cord. 


The  spinal  cord  is  about  one-half  inch  in  diameter, 
being  a  little  thicker  from  side  to  side  than  from  front  to 
back. 

Two  fissures  run  the  whole  length  of  the  cord,  dividing 
it  into  two  equal  jiarts.  The  one  in  front  is  called  the 
anterior  or  ventral  fissure,  and  the  one  behind  is  called  the 
Xjosterior  or  dorsal  fissure.  The  anterior  fissure  is  wider 
and  not  quite  so  deep  as  the  posterior. 

A  cross-section  shows  that  the  cord  is  composed  of 
white  and  gray  matter,  the  white  being  on  the  outside 
and  the  gray  in  the  centre.  This  arrangement,  as  we 
have   seen,   is  just  the  opposite   of   that   in  the  brain. 


TIIK    NF.IJVorS    S  VST  KM  249 

Tlie  wliitc  iii:itt(M-  is  (•oin])()S('(l  cliielly  ol"  iiuMlullated 
nerve-librrs  runnin^^  \i\)  and  down  tlie  conl,  wliilc  tlie 
gray  matter  is  comi^osed  (•hietty  of  nerve-cells.  The  two 
sides  of  the  cord  are  connected,  as  shown  in  Fig.  115, 
by  an  istlinins  of  white  and  gray  matter,  giving  to  the 
gray  a  resemblance  to  the  letter  H.  The  anterior  horns 
of  the  gray  matter  are  blunt,  and  do  not  come  very  close 
to  the  surface  of  the  cord,  while  the  posterior  ones  are 
pointed,  and  reach  almost  to  the  surface. 

In  the  centre  of  the  isthmus,  in  the  Fig.,  is  seen  a 
small  circle.  This  is  a  cross-section  of  a  small  tube  which 
runs  the  whole  length  of  the  cord,  and  opens  above  into 
cavities  called  ventricles  in  the  white  matter  of  the  brain. 

Spinal  nerves. — Thirty-one  pairs  of  spinal  nerves 
issue  from  the  cord  and  pass  out  between  the  vertebrae 


A     ^'^^^'^      ^1 
Fig.  lie. — A  piece  of  spinal  cord.    A^  A,  anterior,  motor,  or  efferent 
nerve-roots ;    P,  P,   posterior,  sensory,   or  afferent  nerve-roots  ;  Gr,  (?, 
ganglia  on  posterior  roots ;  .S",  S,  beginning  of  spinal  nerves. 

to  nearly  all  parts  of  the  body.  On  each  side  of  the  an- 
terior fissure  are  two  shallow  grooves,  and  on  each  side 
of  the  i^osterior  fissure  are  two  similar  grooves.  From 
these  grooves  the  rootlets  of  the  nerves  spring  in  a  close 
longitudinal  row,  as  may  be  seen  in  Figs.  116  and  117.  A 
number  of  these  rootlets  collected  together  constitute  a 
spinal  nerve.     Those  that  spring  from  the  anterior  part 


250 


THIED   BOOK   OF   PHYSIOLOGY 


of  the  cord,  on  each  side  of  the  fissure,  are  motor  nerves o 
Those  which  appear  to  originate  on  the  posterior  i^art  on 
each  side,  are  sensory  nerves.  The  motor  and  sensory 
nerves  from  the  same  half  of  the  cord 
soon  unite  into  one  nerve,  the  two 
kinds  of  nerve-fibres  being  bound  to- 
gether in  the  same  bundle,  and  yet 
remaining  independent  of  each  other 
throughout  their  whole  course. 

On  the  posterior  roots,  just  before 
the}^  unite  with  the  anterior  ones,  is 
an    enlaro:ement,    or    knot,    called   a 


spinal  ganglion.  One  of  these  is  found 
on  each  of  the  posterior  nerve-roots. 
These  are  small  collections  of  nerve- 
cells  with  special  and  important  func- 
tions. 

The  roots  of  the  anterior,  or  motor, 
fibres  arise  from  the  cells  in  the  ante- 
rior horn  of  the  gray  matter,  and  an 
impulse  from  that  source  moves  out  on 
the  different  fibres. 

The  sensory  fibres   arise   from   the 

cells  of  the  spinal  ganglia,  as  shown 

in  Fig.  118.     These  fibres  divide  into 

two,  a  short  distance  from  the  cell, — 

one  branch  running  out  to  the  sensory 

region,  as  the  skin,  and  the  other  branch  joining   the 

spinal  cord  and  passing  up  through  the  white  matter  to 

the  brain.     Here  and  there  along  its  ascent  fine  branches 


Fig.  117.  —  Poste- 
rior view  of  the  upper 
section  of  spinal  cord, 
showing  the  eight 
cervical  nerves. 


TITK    XKKVors    SYSTExM 


251 


are  given  oil"  w iiiili  aiborize  about  the  cells  in  tlie  ante- 
rior horn  of  tlie  gray  matter.  Tliat  is,  the  libre  at  its 
end  divides  into  line  branches,   which   mingle  with  the 


Fig.  118. — Diairrani  showinsr  the  ori2;in  and  relation  of  afferent  and 
efferent  nerves.  .?,  skin  ;  G,  ganglion  ;  P,  posterior  horns  ;  M,  mus- 
cle ;  af,  afferent  nerve  ;  e/,  efferent  nerve  ;  A,  anterior  horns. 

dendrites  of  the  motor  cell,  much  as  the  branches  of  one 
tree  may  mingle  with  those  of  another  when  the  trees 
stand  close  together. 

Nerve  endings. — As  already  exi^lained,  the  neuron 
is  a  cell  which  is  peculiar  in  that  it  may  send  out  a  very 
long  process  of  its  own  material.  The  cell-body  and  its 
nucleus  are  the  central  parts  of  the  neuron  5  the  axis- 
cylinder  process  is  the  line  of  communication  between 
-the  cell-bod}^  and  the  organ  to  which  the  neuron  is  at- 
tached ;  and  the  nerve  ending  is  a  special  arrangement  by 
which  a  nervous  impulse  may  be  readily  communicated 
to  the  cells  of  other  tissues,  or  by  which  an  outside  stim- 
ulus, such  as  light,  sound,  and  touch,  uidy  be  received 
with  distinctness  and  inteusit}'. 

Xot  every  neuron,  however,  is  supplied  with  a  special 
ending.  A  single  nervous  impulse  may  be  transmitted 
over  several   neurons  to  its  destination.     As  shown  in 


252 


THIRD   BOOK   OF   PHYSIOLOGY 


diagram  (Fig.  119),  the  impulse  may  start  from  A  and 
travel  to  B,  thence  on  the  next  neuron  to  C.  and  finally 

reach    the    ending    in   the    muscle 

at  M. 


M 

Fig.  119. — Diagram 
showing  method  by 
which  one  neui'on  may 
communicate  with  an- 
other. 


Motor  end  plates. — At  the 
termination  of  nerves  which  are 
distributed  to  muscles,  the  proto- 
plasm of  the  axis-cylinder  ai^pears 
to  be  poured  out  on  the  muscle- 
fibre  for  a  distance  in  all  directions, 
as  shown  in  Fig.  120.  This  is  called 
the  end  plate  of  the  nerve. 

An  end  plate  is  attached  to  each 
muscle-fibre,  near  its  middle. 

The  nerve-fibre  pierces  the  wall 
of  the  muscle-fibre,  the  neurilemma 
being   joined  to   the   sarcolemma, 


Fig.  120. — End  plate  of  a  motor  nerve- 
fibre. 


and  the  axis-cylinder  of  the  nerre  being  joined  to  the 
protoplasmic   contents  of  the  muscle-cell.     Thus,  a  uer- 


TIIK    NKRVOUS    SYSTEM  253 

vous  impulse  miiy  start  in  a  iiorve-ceiitre,  as  in  the  brain 
or  spinal  cord,  and  Ix'  conducted  alon<;-  a  nerve  to  the 
end  plate,  and  thence  to  the  fibres  of  muscle,  causing 
them  to  contract. 

Endings  of  sensory  nerves. — I  n  case  of  a  sensory 
nerve,  the  stimulus  is  applied  at  the  end  and  the  resulting 
impulse  travels  in  to  the  nerve-centre. 


Fig.  121. — Diagnini  .sliowing  eH)iinection  of  a  nervo-fibre  to  a  cell  of 
muscle.    A^  axis-cylinder  of  nerve  ;  ??,  neurilemma  ;  ?/<,  cell  of  muscle. 

The  office  of  this  set  of  nerves  is  to  keep  the  nerve- 
centres  informed  in  regard  to  the  condition  of  the  body 
and  the  body's  relation  to  outside  objects.  Thus,  when 
any  wound  is  received  or  any  organ  is  diseased,  the  mind 
is  informed  by  impulses  conveyed  on  the  sensory  nerves. 
The  same  set  of  nerves  also  convey  sensations  of  heat 
and  cold  and  pres.suie. 

One  pair  of  this  kind  of  nerves  has  such  delicate 
endings — the  eyes — that  even  waves  of  ether  can  start 
in  them  an  imj)ulse  which  produces  the  sensation  of 
light.  Another  pair  has  the  ears  for  nerve  endings,  and 
waves  of  air  can  start  in  them  an  impulse  which  results 
in  the  sensation  of  sound. 

There  are  five  special  sensory  nerve  endings  producing 
five  special  senses^ — aeeing,  hearing,  feeling^  tasting,  and 


254  TRIED   BOOK   OF   PHYSIOLOGY 

smelling.     These  are  more  fully  described  in  a  separate 
chapter. 

Other  nerves. — Xerves  have  been  classified  as  motor 
and  fiensory  because  these  are  their  chief  functions.  But 
nerves  perform  other  functions  also. 

Secretion  and  excretion  are  vital  operations  and  are 
performed  by  li\ing  cells,  which  are  grouj^ed  together  in 
a  form  which  we  have  called  a  gland.     Xerve-fibres  are 

distributed  to  each  cell  of  a  gland, 
and  the  stimulus  which  comes  to 
them  over  the  nerves  regulates  the 
activity  of  the  gland.  If  such  a  nerve 
be  severed,  the  gland  will  become 
inactive. 


A  nerve  plexus. — A  nerve 
plexus  is  a  point  where  many  nerves 
come  close  together  and  where  fibres 
branch  off  from  one  nerve  and  con- 
tinue their  way  in  another  nerve. 

Fig.  122. —Mode  Xerve-fibres  do  not  form  a  net- 
of  branching  of  nerve- 

fi^j-eg  work,  like  blood  capillaries,  but,  as 

shown  in  Fig.  122.  fibres  leave  one 
bundle  and  join  another.  Xumerous  branches  of  this 
kind  occur  in  the  plexuses. 

The  nerve  which  comes  from  a  plexus  may  thus  be 
put  in  communication  with  many  nerve-centres.  In  this 
way  the  parts  of  the  body  to  which  such  nerves  are  dis- 
tributed, for  example,  the  legs,  are  capable  of  a  great 
variety  of  movements. 


THE   NERVOUS   SYSTEM  255 

Nnnierous  plexuses,  some  large  and  some  small,  are 
fouml  tlirougiiout  llie  nervous  sj'stem.  The  chief  ones 
are  found  in  tlie  neck,  the  regions  of  the  pelvis,  and 
associated  with  the  sympathetic  system  in  the  cavities 
of  the  thorax  and  abdomen. 

The  sympathetic  nervous  system. — The  sym- 
pathetic nervous  system  is  chielly  concerned  in  the  stimu- 
lation and  control  of  tfie  involuntary  processes. 

It  is  called  sympathetic  because  of  the  close  relation 
or  sympathy  which  these  nerves  establish  between  many 
vital  organs  of  the  body.  For  example,  increased  mus- 
cular effort  calls  for  more  blood,  the  arteries  relax,  and 
the  heart  lesponds  by  beating  faster.  This  calls  for  more 
oxygen,  and  breathing  is  hastened.  The  product  of  this 
increavsed  combustion  must  be  cared  for  by  an  increased 
activity  of  the  excretory  glands. 

Thus,  by  means  of  the  connecting  nerves,  one  organ  is 
made  to  work  in  harmony  with  another. 

The  sympathetic  system  consists  of  ganglia,  nerves,  and 
plexuses.  The  chief  ganglia  are  forty-nine  in  number 
and  are  arranged  in  two  rows,  one  on  each  side  of  the 
spinal  column  and  a  little  to  the  front  of  it.  Each  gang- 
lion is  connected  by  a  nerve  to  the  one  above  it  and  to 
the  one  below  it,  giving  to  the  whole  the  appearance  of 
two  chains  hung  from  the  base  of  the  cranium,  with  their 
lower  ends  connected  at  the  coccyx.  Thus,  there  are 
twenty-four  ganglia  on  each  side  and  one  at  the  bottom 
midway  between,  and  to  which  the  lower  ends  of  the  two 
chains  are  attached. 


256  THIED   BOOK   OF   PHYSIOLOGY 

The  nerves  of  the  sympathetic  system  are,  for  the  most 
part,  non-medullated,  and  so  are  finer  and  of  a  grayish 
color. 

Along  with  these  nerves  are  mingled  many  branches 
of  the  spinal  and  cranial  nerves,  so  that  the  whole  ner- 
vous system  is  intimately  connected. 

The  sympathetic  nerves  are  distributed  to  the  viscera 
of  the  thorax  and  abdomen,  to  the  blood-vessels,  and  to 
the  lymphatics. 

In  front  of  the  chains  of  ganglia  are  three  great 
plexuses  of  nerves  containing  numerous  smaller  ganglia. 
The  one  in  the  thorax  is  called  the  cardiac  plexus.  The 
one  in  the  abdomen  is  called  the  solar  plexus.  It  is  just 
back  of  the  stomach  and  has  smaller  plexuses  radiating 
from  it,  the  whole  resembling  somewhat  the  sun  and  its 
rays,  and  hence  its  name.  The  one  in  the  pelvis  is 
called  the  hypogastric  plexus. 

QUESTIONS  FOR  REVIEW. 

1.  Why  does  the. body  need  a  controlUng  organ?    Ihustrate. 

2.  Compare  the  body  as  an  organism  with  an  organized  body 
of  men. 

3.  Of  what  parts  is  the  nervous  system  composed? 

4.  What  three  kinds  of  nerve-centres? 

5.  What  are  the  two  great  nervous  systems?     Of  what  is  each 
composed  ? 

6.  Describe  a  nerve-ceh. 

7.  AVhat  is  the  unit  of  the  nervous  system? 

8.  Describe  the  axis-cylinder  and  its  sheaths. 

9.  What  makes  a  nerve-fibre  white? 

10.  How  does  the  gray  differ  from  the  white  matter  of  tlie  ner- 
vous system  ? 


TITF    M:iJ\'()rS    SYSTK.M  257 

11.  W\\&t  \i^  iietirogl id  f 

12.  What  is  the  ^rain/     Describe  ita  coverings. 

].'>.  What  is  meant  by  "the  pin  inatrr  \<  a  vtu^cnlar  iiM-rnbrane"  ? 

14.  What  is  cerebrospinal  7neningiti.<t  f 

15.  What  is  the  weight  of  the  human  brain? 

1«).   What  are  the  principal  divisions  of  the  brain? 
17.  Describe  the  cerebrum  as  to  its  fissures,  hemispheres,  lobes, 
convolutions,  and  cortex. 

IS.  Describe  the  structure  of  the  cerebellum. 

19.  Describe  the  poiis. 

20.  What  is  the  medulla  oblongata,  and  of  what  is  it  composed? 

21.  Describe  the  structure  of  a  nerve. 

22.  How  lai^e  are  nerves  ? 

23.  Compare  a  nerve  to  a  telephone  cable. 

24.  What  are  the  two  kinds  of  nerves,  and  how  do  they  differ? 

25.  How  many  pairs  of  cranial  nerves  f    To  what  parts  of  the 
body  are  they  chiefly  distributed? 

2f>.  Describe  the  pneumogasiric  nerves. 

27.  How  is  the  spinal  cord  protected  ? 

28.  Make  a  drawing  and  explain  the  appearance  of  a  cross-section 
of  the  spinal  cord. 

29.  How  many  spinal  nerves  ? 

30.  What  are  the  roots  of  spinal  nerves,  and  what  two  kinds  ? 

31.  Which  roots  have  ganglia? 

32.  Explain   how  the  two  kinds  of    nerves   connect  with   the 
spinal  cord. 

33.  What  are  yiene  endings  f 

34.  Describe  a  motor  end  plate. 

35.  What  kind  of  endings  on  the  sensory  nerves? 

36.  Explain  a  nerve  plexus. 

37.  In  what  way  does  one  nerve  branch  to  another? 

38.  Why  is  the  sympatJietic  system  so  called? 

39.  Of  what  is  the  sympathetic  system  composed? 

40.  Describe  the  solar  plexus. 

17 


CHAPTEE   XVI 

PHYSIOLOGY   OF   THE   NERVOUS   SYSTEM. 

Some  functions  of  the  nervous  system  have  already 
been  alluded  to  in  the  preceding  chapter  to  make  plainer 
the  anatomy  of  the  part  described.  This  chapter  will  be 
devoted  entirely  to  a  brief  description  of  some  of  the 
fundamental  functions  of  the  system  as  far  as  known. 

Little  by  little  many  important  facts  about  nerve- 
centres  and  nerves  have  been  discovered,  but  as  yet 
much  is  unknown  both  about  their  anatomy  and  their 
physiology.  It  is  known,  for  example,  that  the  mind  is 
in  some  way  intimately  associated  with  the  brain  :  but  we 
have  not  even  a  plausible  theory  as  to  the  nature  of  the 
association.  It  is  known  that  some  kind  of  an  impulse 
passes  from  cells  over  nerves  ;  but  nothing  is  known  as  to 
the  nature  of  the  impulse.  It  is  known  that  an  impulse 
may  be  transmitted  from  one  neuron  to  another ;  but  it 
is  not  known  how  this  is  accomplished. 

All  such  facts  will  doubtless  be  satisfactorily  explained 
when  the  related  sciences  have  advanced  far  enough  to 
make  such  things  intelligible. 

Four  functions  of  nerve-centres. — Collections 
of  nerve-cells,  forming  nerve-centres,  are  the  essential 
parts  of  the  nervous  system,  the  nerves  being  simply  the 
carriers  of  nervous  impulses. 

258 


TIIK    NRRVOUS    SVSTKM  259 

Tlie  functions  of  these  centres  may  be  classified  ;is  four 
kinds.  (1)  They  ore  rrcfirer.s  of  imjmJsr.s  hvow/ht  fo  them 
over  afferent  nerves.  The  elfeet  of  the  impulses  is  a  sensa- 
tion of  which  tlic  niin<l  uvax  or  may  not  become  con- 
scious. (2)  Thei/  (ire  the  origin  of  iinputses  which  cause  a 
contraction  <f  )nn.seles.  Thus,  all  movement  of  the  body 
is  under  the  control  of  the  nerve-centres.  (3)  They  direct 
and  control  nutrition^  secretion,   excretion,   and  distribution. 

0 

(4)  The  highest  function  of  any  nerve-centre  is  that  of  think- 
ing, hnoicing,  feeling,  ivilling,  and  remembering,  all  of  which 
are  in  some  way  connected  with  the  cerebrum.  These  mental 
operations  are  functions  of  the  cerebrum  only  in  the  sense 
that  mind  operates  through  the  matter  of  that  centre. 

Function  of  the  cerebrum. — It  has  been  esti- 
mated that  the  gray  matter — the  cortex  of  the  cerebrum 
— contains  over  9,000,000,000  nerve-cells.  The  functions 
of  this  great  nerve-centre  are  the  most  important  per- 
formed by  a  human  being,  and  are  the  distinguishing 
marks  between  man  and  all  other  animals. 

The  cerebrum  is  the  centre  for  all  mental  operations.  It 
is  there  that  we  are  conscious  of  our  existence  and  of  what 
w^e  are  doing.  It  is  there  that  we  study,  think,  imagine f 
and  remember. 

All  such  mental  operations  are  probably  accomj^lished 
by  all  the  gray  matter  of  the  cerebrum  working  together. 
In  the  anatomy  of  the  cerebrum  it  was  explained  that 
numerous  fibres  connected  the  hemispheres,  lobes,  and 
convolutions  of  the  cerebrum.  By  means  of  these  the 
cerebrum  may  act  as  a  unit. 


260 


THIED    BOOK   OF    PHYSIOLOGY 


Localization  of  functions. — Two  other  great  func- 
tions of  the  cerebrum  are  volition  and  sensation.  These 
are  more  or  less  limited  to  certain  areas  of  the  cortex. 
For  example,  one  area  may  be  a  centre  for  the  movements 


W    0 


0     R 


Fig.  123. — Diagram  showing  the  location  of  the  motor  and  sensory 
areas.  It  will  he  noticed  that  the  motor  areas  are  in  the  central  region 
of  the  cortex,  and  the  sensory  areas  are  in  the  posterior  parts. 

of  the  arm,  and  another  for  movements  of  the  leg.  One 
area  may  receive  sensory  impulses  from  the  eye  and 
another  from  the  ear.  Thus  there  is  a  division  of  labor 
among  the  cells,  each  area  performing  a  definite  function 
peculiar  to  itself. 

By  numerous  experiments,  many  of  these  areas  liave 


THE    XFRVOUS   SYSTEM  261 

been  mapped  out.  If  tliroii^h  accident  the  skull  is  loade 
to  press  upon  certain  portions  of  the  cortex,  it  Ls  ob- 
served that  some  portion  of  the  body  loses  sensation  or 
the  j)Ower  of  motion — that  is,  l>ecomes  paralyzed.  Some- 
times a  blood-clot  becomes  lodged  over  certain  parts  of 
the  brain,  and  similar  results  follow.  In  such  cases,  if 
the  cause  of  the  pressure  be  removed,  the  part  of  the 
body  that  was  affected  will  regain  its  normal  condition. 

Experiments  have  al9<5  l)eeu  made  upon  the  monkey's 
brain,  which  most  resembles  the  human,  and  when  an 
electric  stimulus  is  applied  to  various  points  on  the  cor- 
tex, it  is  observed  that  different  parts  of  the  body  are 
caused  to  move.  Thus,  when  one  point  is  touched,  the 
fingers  will  close.  At  other  points  the  arms,  legs,  or  toes 
will  be  aflfecteil. 

In  this  way  the  cortex  has  been  mapped  out  into  motor 
areas,  as  represented  in  Fig.  123. 

The  sensory  regions  are  not  so  definitely  determined. 
The  sensation  of  vision  is  located  in  the  occipitiil  lobe  of 
the  cerebrum,  the  region  of  hearing  is  iust  in  front  of  it. 
and  taste  and  smell  are  located  in  the  temporal  lobes. 

Tne  cerebrum  as  the  controlling  organ. — 
The  muscles  uf  the  body  may  receive  a  stimulus  from 
several  different  nerve-centres,  but  all  voluntary  acts 
have  their  origin  in  the  cerebrum.  Tlie  cerebrum  is  the 
centre  of  all  voluntary  motion. 

Sensory  impulses,  also,  may  never  reach  the  cerebrum, 
or  may  be  unheeded  there,  but  all  cautious  sensation  is  in 
the  cerebrum. 


262  THIRD   BOOK   OF   PHYSIOLOGY 

While  the  cerebrum  acts  as  a  unit  in  the  higher  func- 
tions of  thinking  and  knowing,  each  lieinisphere  exer- 
cises complete  control  over  the  opposite  side  of  the 
body,  and  through  the  sympathetic  system  may  even 
greatly  modify  the  involuntary  movements. 

Impulses  carried  over  a  seusory  nerve  may  produce  a 
conscious  sensation,  and  the  motor  nerves  may  then  at 
once  carry  a  stimulus  to  the  muscles,  and  thus  execute  a 
volition.  The  sensation  may,  however,  be  stored  in  the 
meraorj^  and  not  acted  upon  for  weeks  or  years.  Man, 
in  this  respect,  differs  from  animals,  which  are  in  most 
instances  creatures  of  sudden  impulse. 

Intelligence  and  the  size  of  the  brain.— Other 

things  being  equal,  intellectual  power  is  i)roportional  to 
the  size  of  the  brain.  Size  alone,  however,  is  no  proof 
of  a  superior  intellect.  Men  whose  braius  were  of  aver- 
age size  have  often  shown  themselves  superior  in 
thought  to  others  who  had  a  large  head.  The  texture 
and  area  of  the  cortex  of  the  cerebrum  seem  to  have 
most  to  do  with  the  character  of  a  man's  mental  endow- 
ment. 

Function  of  the  cerebellum. — The  function  of 
the  cerebellum,  as  far  as  known,  is  chiefly  to  harmonize 
and  coordinate  the  various  movements  of  the  body. 
The  act  of  balancing  the  body  and  retaining  the  proper 
position  in  standing  or  walking  or  performing  any  act  in 
which  many  muscles  are  engaged  is  j^erformed  by  the 
cerebellum.     When  this  part  of  the  brain  is  injured  the 


THK    NKRVOUS   SYSTPLM  263 

sense  of  o<iiiilibrium  is  lost,  and  one  will  stagger  like  a 
drunken  man  when  he  attempts  to  walk.  The  cerebrnm 
can  still  order  any  movement  as  before,  but  the  muscles 
will  not  act  in  harmony,  and  so  the  execution  of  the 
"movement  will  be  extremely  awkward. 

Function  of  the  pons.— As  might  be  inferred 
from  the  anatomy  of  the  pons,  it  is  chiefly  a  passage-way 
for  nerves  from  various -parts  of  the  nervous  system.  It 
contains,  however,  a  considerable  quantity  of  gray  mat- 
ter, and  no  doubt  is  the  origin  of  some  important  func- 
tions besides  being  simply  a  medium  of  communication. 

General  functions  of  the  medulla  oblongata 
and  the  spinal  cord. — Since  the  medulla  is  properly 
a  continuation  of  the  spinal  cord,  they  have  functions 
which  are  common  to  both.  The  first  is  tlie  transmission 
of  impulses  over  the  fibres  of  white  matter  to  and  from  the 
brain.  These  fibres  cross  in  the  medulla  to  opposite 
sides,  so  that  if  they  be  severed  on  the  right  side  above 
the  point  of  crossing,  the  left  side  of  the  body  will  be 
paralyzed.  If  they  be  severed  on  the  right  side  below 
the  point  of  crossing,  the  right  side  of  the  body  will  be 
paralyzed.  3Iost  of  the  motor  impulses  from  the  brain 
pass  through  the  white  matter  of  the  medulla,  spinal 
cord,  and  spinal  nerves  to  the  muscles,  glands,  and  cells 
of  the  body.  Along  this  same  route,  though  on  different 
fibres,  many  of  the  sensory  impulses  come  to  the  brain. 

The  second  important  function,  common  to  both,  is 
reflex  action. 


264  THIRD   BOOK   OF   PHYSIOLOGY 

The  action  is  called  reflex  when  a  sensory  impulse  is 
sent  in  to  a  centre  in  the  medulla  or  cord,  and  from  that 
centre  a  motor  impulse  is  sent  out  to  a  muscle  or  gland 
without  the  knowledge  or  action  of  the  cerebrum.  By 
reference  to  Fig.  118  the  circuit  of  a  reflex  action  can  be 
seen.  A  sensation  starting  at  the  skin  is  conveyed  by 
an  afferent  nerve  to  the  cord,  where  a  branch  from  the 
nerve  communicates  with  cells  in  the  anterior  horn  of 
the  gray  matter,  and  these  cells  send  back  a  motor  im- 
pulse on  an  efferent  nerve  to  the  muscle.  Thus  a  reflex 
action  is  a  short-cut  from  a  sensory  region  to  nerve- 
centre  and  back  to  muscle. 

By  reference  to  the  illustration  in  the  second  para- 
graph of  Chapter  XV  it  can  now  be  seen  that  these 
centres  of  reflex  action  correspond  closely  to  the  heads 
of  departments  in  the  organized  body  of  men.  In  most 
of  the  ordinary  matters  no  report  is  made  to  the  presi- 
dent of  the  organization,  but  only  to  the  head  of  the  de- 
partment, and  he  at  once  sends  out  the  proper  orders. 
If  anything  unusual  happens,  then  a  report  is  made  to 
the  head  of  the  whole  organization, — the  president.  In 
the  same  way  all  ordinary  routine  matters  of  the  body 
are  attended  to  by  the  reflex  centres  ;  but  when  any- 
thing arises  which  requires  thought,  deliberation,  or 
choice,  the  whole  matter  is  referred  to  the  cere- 
brum. 

The  afferent  nerve  continues  its  way  up  the  cord  to 
the  brain,  so  that  the  same  impulse  may  produce  con- 
scious sensation,  and  additional  motor  impulses  may  be 
sent  out  by  the  overruling  cerebrum. 


THE    .\HIiVOUS   SYSTKM  205 

Examples  of  reflex  action.  -  A  man  whose  spinal 
cord  is  broken  or  diseased  in  the  dorsal  region  will  still 
move  his  legs  violently  if  the  bottoms  of  his  feet  are 
tickled.  The  tickling  could  not  produce  any  conscious 
sensation,  for  all  connection  with  the  cerebrum  is  sev- 
ered. A  centre  in  the  lower  part  of  the  cord  receives 
the  sensory  impulse  from  the  foot  and  at  once  sends 
back  on  a  motor  fibre  an  impulse  which  causes  the  con- 
traction of  the  muscles.  '  It  is  evident  from  these  facts 
that  certain  nerve-centres  may  receive  and  send  out  ner- 
vous impulses  without  the  knowledge  or  interference  of 
the  brain. 

Such  action  is  of  constant  occurrence  in  the  normal 
body.  If  the  hand  touch  a  hotobject,  it  will  almost  in- 
stantly be  pulled  away.  One  will,  even  while  uncon- 
scious in  sleep,  brush  a  fly  from  his  face  ;  and  although 
such  action  is  not  a  result  of  a  conscious  effort  of  the  will, 
yet  it  is  directed  in  accordance  with  a  definite  i)urpose. 

The  presence  of  food  in  the  mouth,  or  even  the  sight 
of  food,  may  cause  an  impulse  to  be  sent  out  to  the 
glands  which  secrete  saliva  or  other  digestive  juices. 
Such  action  is  purely  reflex  and  requires  no  efl'ort  of  the 
mind. 

Special  functions  of  the  medulla.— The  medulla 
contains  some  of  the  most  important  reflex  centres.  The 
whole  brain  above  the  medulla  may  be  removed,  and  the 
animal  so  treated  will  continue  to  live,  but  without  sen- 
sation or  volition.  Sucli  an  animal  will  continue  his 
breathing  in  the  ordinary  manner,  his  heart  will  continue 


266  THIKD    BOOK   OF   PHYSIOLOGY 

to  beat,  and  other  vital  functions  will  be  performed  as 
before,  but  he  will  remain  in  one  spot  until  he  starves  to 
death.  If,  however,  he  be  touched,  he  will  move.  If 
food  be  placed  on  the  back  of  his  tongue,  he  will  swallow. 
These  are  purely  reflex  actions. 

If,  now,  the  medulla  be  destroyed,  death  will  follow 
Immediately,  for  in  the  medulla  is  the  "vital  knot,"  or 
nerve-centre,  which  operates  breathing.  This  centre  is 
even  stronger  than  the  will  itself,  for,  although  we  may 
voluntarily  stop  breathing  for  a  time,  yet  it  will  soon 
begin  in  spite  of  any  effort  of  the  will. 

In  the  medulla  is  another  centre  which  regulates  the 
beating  of  the  heart,  causing  it  to  beat  faster  or  more 
slowly  as  the  need  may  be.  Another  important  centre 
there  is  the  vasomotor  centre,  which  causes  the  walls  of 
the  arteries  to  contract  or  relax,  thus  regulating  the 
supply  of  blood  to  various  parts  of  the  body.  Still 
others  are  the  sneezing,  coughing,  and  vomiting  centres. 

The  medulla  is  the  great  centre  of  those  reflex  actions  upon 
which  the  maintenance  of  life  depends. 

The  economy  of  life  in  reflex  action.— If  every 
sensory  impulse  had  to  go  to  the  cerebrum,  and  every 
motor  impulse  had  to  come  from  it,  the  mind  could  do 
little  else  than  attend  to  the  ordinary  routine  matters  of 
life,  and  would  do  that  very  poorly.  It  is  much  better, 
as  nature  has  fixed  it,  to  have  certain  centres  which 
become  expert  in  doing  those  things  which  are  repeated 
again  and  again.  In  this  way  the  mind  is  free  to  devote 
itself  to  a  consideration  of  higher  and  more  important 


TIIK   NF^:RV0TTS   system  267 

matters.  Thus  a  student  can  concentrate  his  whole  mind 
upon  the  solution  of  a  problem,  and  other  nerve-centres 
will  look  after  the  breathing,  digestion,  excretion,  and 
the  flow  of  blood. 

Not  only  is  there  economy  of  life  in  having  lellex 
centres  to  perform  the  vital  functions,  but  also  many  of 
the  acts,  which  at  first  re(iuired  a  conscious  effort,  may 
and  should  become  reflex.  Those  actions,  which  are 
repeated  again  and  again  through  life,  should  be  made 
automatic  as  completely  as  possible.  Such  actions  as 
walking,  writing,  playing  a  musical  instrument,  proper 
forms  of  speech,  dressing,  and  all  actions  which  are  con- 
stantly repeated  in  any  occupation  in  which  one  is 
engaged,  should  be  automatic. 

Education  of  reflex  centres.— Some  of  the  reflex 
centres,  especially  those  in  the  medulla,  were  born  with 
us  in  full  power  of  operation.  These  are  indispensable 
to  the  maintenance  of  life.  Many  other  centres  in  the 
cord  and  brain  are  capable  of  education. 

The  first  efforts  at  walking  require  a  close  attention  of 
the  mind,  but  by  repeated  efforts  the  action  becomes 
reflex  and  automatic.  Then,  when  the  motion  of  the  legs 
is  once  started,  the  walking  will  be  continued,  though 
the  mind  be  directed  to  other  matters. 

Writing  at  first  is  a  laborious  process,  taking  the  full 
attention  of  the  child,  but  later  the  hand  makes  the 
letters  while  the  mind  is  attending  to  the  thought. 

The  first  attempt  to  play  a  violin  is  awkward,  and  the 
mind  must  attend  every  movement  of  the  fingers,  but  by 


268  THIRD    BOOK    OF   PHYSIOLOGY 

constant  repetition  the  action  becomes  reflex,  and  thought 
can  then  be  given  to  harmony  and  expression. 

Even  sach  matters  as  tying  shoe-strings  or  a  neck-tie 
become,  by  frequent  repetition,  purelj'  automatic. 

Habit. — Habit  is  an  acquired  disposition  to  act  or 
think  in  a  certain  way.  It  may  easily  be  inferred  from 
what  is  said  in  the  x>receding  paragraph  that  habit  is 
formed  by  frequent  repetition  of  the  same  act  or  thought. 

A  habit  may  be  of  the  greatest  advantage  or  disadvan- 
tage to  its  possessor. 

The  character  and  mode  of  action  of  the  nervous  system 
furnishes  the  basis  for  an  explanation  of  the  formation  of 
habit. 

Several  rei)etitions  of  the  same  act,  in  response  to  any 
stimulus,  will  make  it  easier  for  that  same  stimulus  to 
result  in  a  similar  act.  For  illustration,  when  a  boy  is 
being  taught  that  he  should  lift  his  hat  when  he  meets  a 
lady,  he  may  have  to  be  reminded  of  the  fact  a  njmbei 
of  times  at  first,  but  after  many  repetitions  of  the  act  he 
will  perform  it  without  any  thought  whenever  the  occa 
sion  arises. 

One  who  has  often  wet  his  fingers  or  thumb  in  his 
mouth  when  he  wished  to  turn  the  leaves  of  a  book  is 
quite  sure  to  employ  that  method  when  he  reads  a  paper 
or  book  before  an  audience. 

The  motor  impulses  come  to  act  in  certain  grooves,  as 
it  were,  and,  unless  the  dominant  cerebrum  is  able  to  over- 
power and  direct  these  impulses  in  new  channels,  the  habit 
becomes  fixed. 


TIIK    NKIJVorS    SVSTFM  2f)9 

Functions  of  nerves.— Nerves  are  tlie  conductors 
of  nervous  impulses.  While  the  niiturc  of  the  impulse  is 
not  known,  its  various  effects  an^  doubtless  due  to  the 
character  of  the  orpin  which  receives  it,  just  as  a  cur- 
rent of  electricity  will  produce  sound  in  a  telephone, 
light  in  an  electric  lamp,  motion  in  a  motor,  or  elec- 
trolysis in  certain  chemical  compounds. 

The  various  sensory  organs  receive  stimuli  from  the 
outside,  and  the  afferent  nerves  carry  them  to  the  nerve- 
centres. 

The  efferent  nerves  carry  orders  from  the  nerve-centres, 
and  their  effect  may  be  a  contraction  of  muscles,  secre- 
tion of  the  glands,  nutrition  of  the  cells,  or  a  regulation 
of  the  rapidity  and  frequency  of  muscular  contraction, 
as  in  the  heart. 

Each  fibre  of  a  nerve  has  its  own  special  work  to  do, 
and  if  it  is  disabled  the  other  fibres  near  by  cannot 
assume  its  work.  If  a  small  part  of  the  liver  or  lungs 
should  be  injured,  the  remaining  part  can  completely 
perform  the  functions  of  those  organs ;  but  if  a  single 
fibre  of  the  optic  nerve,  for  example,  should  be  severed, 
a  blind  spot  will  be  produced  in  the  eye. 

QUESTIONS   FOR  REVIEW. 

1.  Give  four  functions  of  nerve-centres. 

2.  What  makes  the  cerebrum  such  an  important  centre? 

3.  In  what  part  of  the  cerebrum  do  we  think? 

4.  Name  several  mental  operations  that  are  performed  in  the 
cerebrum. 

5.  Explain  what  is  meant  by  the  localization  of  functions.  How 
was  this  determined? 


270  THIRD   BOOK   OF   PHYSIOLOGY 

6.  Give  the  locality  of  several  motor  areas  in  the  cortex  of  the 
cerebrum.     Also  locate  several  sensory  areas. 

7.  What  is  voluntary  motion,  and  where  is  its  centre? 
S.  Where  do  we  become  conscious  of  a  sensation? 

9.  "Why  does  an  injury  to  the  right  side  of  the  brain  paralyze 
the  left  side  of  the  body  ? 

10.  "What  is  meant  by  saying  that  wild  animals  are  creatures  of 
sudden  impulse? 

11.  AVhat  relation  is  there  between  the  size  of  the  brain  and 
mental  capacity? 

12.  What  is  the  chief  functioii  of  the  cerebellum? 

13.  Of  what  use  is  the  pons? 

14.  What  two  important  functions  are  common  to  the  medulla 
and  the  spinal  cord  ? 

15.  Explain  fully  a  reflex  action. 

16.  Give  several  examples  of  reflex  action. 

17.  Explain  how  centres  of  reflex  action  are  like  heads  of  de- 
partments in  a  large  store. 

18.  Describe  the  important  functions  of  the  medulla. 

19.  What  class  of  reflex  actions  are  centred  in  the  medulla? 

20.  State  fully  the  advantage  of  reflex  action. 

21.  How  can  reflex  centres  be  educated? 

22.  What  is  a  habit? 

23.  Explain  how  habits  are  formed. 


CHAPTEK    XVII 

HYGIENE   OF  THE   NERVOUS  SYSTEM 

Nutrition  of  nervous  tissue. — The  brain,  as  well 
as  other  nervous  tissue,  is  directh'  de})endent  on  the  food 
which  we  eat  for  its  well-being  and  its  ability  to  perform 
its  functions. 

It  is  not  known  just  how  nerve  tissue  appropriates  its 
food,  but  it  is  clear  that  when  the  supply  of  food  is  in- 
adequate, or  the  blood  is  for  any  reason  impoverished 
or  poisoned,  the  nerve  tissue  will  suffer  in  common  with 
the  rest  of  the  body. 

This  is  a  fundamental  fact  in  considering  the  relation 
between  a  health}-  bodj'  and  a  vigorous  mind.  All  food 
must  be  properly  prepared  by  the  organs  of  digestion, 
secretion,  and  excretion,  and  then  properly  distributed 
by  the  organs  of  circulation  before  it  is  ready  for  assimi- 
lation by  the  nervous  tissue  or  any  other  tissue.  A 
healthy  nervous  tissue  is  then  possible  only  when  other 
organs  of  the  body  can  supply  to  it  good  and  sufficient 
nourishment.  It  is  not  necessary  to  a  strong  mind  that 
the  muscles  be  strong  and  that  a  man  be  able  to  perform 
heavy  manual  labor,  but  it  is  necessary  that  the  other 
organs  be  able  to  perform  their  functions. 

Expenditure  of  energy  in  nervous  opera- 
tions.— Every  impulse  sent  out  by  a  nerve-centre  iu- 

271 


272  TRIED    BOOK   OF   PHYSIOLOGY 

volves  an  expenditure  of  energy.  Every  tliought  which 
passes  through  the  mind,  and  every  mental  effort  in  the 
solution  of  a  problem  or  in  pursuance  of  a  line  of  thought, 
uses  up  some  of  the  store  of  energy  in  the  brain.  The 
only  source  of  this  energy  is  the  food  which  we  eat  and 
the  air  which  we  breathe.  Just  as  a  muscle  becomes 
fatigued  when  its  store  of  energy  runs  low,  so  a  nerve- 
centre  can  work  only  when  it  has  a  stock  of  energy  to 
expend. 

The  brain  a  favored  organ. — All  the  other 
organs  are  helpless  without  the  direction  of  the  brain. 
Such  actions  as  breathing  and  the  beating  of  the  heart 
will  continue  for  a  time  without  any  directions  from  the 
cerebrum,  but  all  voluntary  action  will  cease,  and  the 
whole  body,  if  left  to  itself,  will  soon  be  without  food,  and 
so  without  any  store  of  energy  to  expend.  The  natural 
result  is  death,  which  in  this  case  would  simply  mean 
that  the  store  of  energy  had  run  out,  and  consequently 
no  further  activity  could  be  possible. 

For  this  reason  every  effort  is  made  by  the  body  t6 
protect  and  keep  strong  the  master  organ, — the  brain. 

By  referring  again  to  the  organized  company  of  men 
which  we  have  used  for  illustration,  it  is  plain  that  the 
life  and  health  of  the  president,  if  he  is  a  good  one, 
should  be  preserved  for  the  sake  of  every  other  member 
of  the  organization.  Mnch  more  so  is  this  true  of  the 
brain,  for  no  other  organ  can  by  any  means  be  elected 
to  its  place. 

So  we  find  the  brain  well  protected  from  any  chance 


1IY(JIENE   OF   THE    NERVOUS   SYSTEM     273 

injury,  uiid  it  also  appears  that  the  other  organs  will, 
when  necessary,  sacrifice  some  of  their  store  of  energy 
for  the  sustenance  of  the  brain,  acting,  as  it  were,  on  the 
principle  tliat  if  the  brain  should  fail,  all  would  fail 
with  it. 

Proper  kind  of  food  for  the  brain. — Much 
stress  has  sometimes  been  laid  on  the  necessity  of  certain 
kinds  of  food  for  the  support  of  particular  tissues.  One 
kind  for  the  brain,  another  for  the  muscle  or  the  bone, 
and  so  on.  While  this  is  true  to  some  extent,  yet  it  is 
fortunate  that  we  do  not  at  each  meal  have  to  determine 
the  needs  of  the  various  tissues,  and  then  make  out  a 
bill  of  fare  to  supply  those  needs. 

Any  good,  mixed  diet  contains  the  elements  necessary 
for  the  sustenance  of  the  brain.  Besides,  we  cannot 
conclude  that  because  certain  chemical  compounds  are 
found  in  a  tissue,  that  therefore  we  should  eat  foods 
which  contain  those  compounds ;  for  the  cells  of  the 
various  organs  are  able  to  form  many  new  chemical  com- 
pounds from  the  food  material. 

The  important  matters  to  be  considered  are  that  the 
food  be  healthful  for  the  whole  body  ;  that  it  be  well 
masticated  and  digested  ;  that  it  be  distributed  in  the 
blood  to  points  where  it  is  needed  ;  that  it  be  completely 
oxidized  ;  and.  last,  that  the  products  of  the  oxidation  be 
completely  removed  by  excretion. 

When  all  these  are  performed  in  a  natural  way,  the 
brain  will  receive  its  proper  nourishment  without  further 
attention  on  our  part. 

18 


27-t 


THIRD   BOOK   OF   PHYSIOLOGY 


The  supply  of  blood  to  the  brain.— ^Ve  have 

tried  to  emphasize  the  fact  that  every  nervous  impulse 
and  every  process  of  thinking  involve  an  expenditure 
of  energy  which  is  obtained  from  food.  The  average 
brain  constitutes  only  about  one-fiftieth  of  the  weight 


imfpj 


Fig.    124. — The  carotid  artery  conducting:  I'lood  to  the  head.      C,  right 
carotid  ;   I.  internal  carotid  :    E.  external  carotid. 


of  the  body,  but  about  one-eighth  of  the  blood  is  sent  to 
it  for  its  nourishment.  The  internal  carotid  artery,  as 
seen  in  the  figure,  one  on  each  side,  passes  in  through 
the  base  of  the  cranium,  and  is  distributed  through  the 
vascular  pia   mater   to   the   brain -cells.      If  the   blood 


IIVCIKNK    OF   THE    XKRVOUS   SYSTEM     275 

should  be  witlidrawu.   unconsciousness  would  result   at 
once,  and  in  a  short  time  death. 

This  close  dependence  of  mental  action  upon  the  blood 
supply  makes  it  clear  that  the  blood  should  be  rich  in 
those  materials  which  are  loaded  with  energy,  and  also 
free  from  alcohol,  nicotine,  opium,  and  all  other  .sub- 
stances that  have  an  injurious  effect  upon  the  nervous 
tissue. 


Brain  fatigue. — A    machine   cannot   give   out   any 
energy  until  it  first  receives  it.      That  is,  it  cannot  do 


Fig.   125. — .4.  a  cell  stored  with  energy-yielding  material:  B.  same 
cell  fatigued  after  a  period  of  work. 

any  work  until  work  is  done  upon  it.  A  clock  will  not 
run  until  it  is  wound  up.  If  you  will  transfer  enough 
of  your  energy  to  a  clock -spring  to  keep  it  running  for 
eight  days,  the  clock  will  come  to  rest  at  the  end  of  that 
time  only  l^ecause  the  store  of  energy  which  it  received 
from  you  has  then  been  expended. 

The  cells  of  our  bodies  are  little  machines  in  this 
respect.  They  can  convert  energy  which  was  in  food 
into  other  forms,  such  as  motion  and  heat,  but  they  can- 


276  THIRD    BOOK    OF   PHYSIOLOGY 

not  expend  any  more  than  they  receive.  This  is  just  as 
true  of  nerve-cells  as  of  any  cells  of  the  body. 

It  is  j)lain,  then,  that  after  cells  have  been  at  work  for 
a  time  their  store  of  energy  will  be  expended,  and  the 
cells  will  become  fatigued. 

The  condition  of  a  fatigued  cell  can  actually  be  ob- 
served by  means  of  a  microscope.  As  seen  in  Fig.  125, 
the  cell  at  first  is  round  and  plump,  but  after  a  season  of 
work  it  became  jagged  and  shrivelled.  The  cell  can  now 
be  stored  again,  and  will  then  be  able  to  do  more  work. 
Thus  the  cell  is  like  the  clock-spring,  and  if  they  are 
regularly  re-stored  with  energy  they  will  continue  to  run 
until  worn  out. 

Need  of  sleep. — Cells  may  be  receiving  and  expend- 
ing energy  at  the  same  time,  or  they  may  rest  and  store 
up  an  excess  of  energy,  which  may  be  rapidly  expended 
later. 

Man  and  all  animals  are  so  constituted  that  periods  of 
complete  rest  in  sleep  are  absolutely  necessary.  Some 
organs  of  the  body,  as  the  muscles,  may  get  partial  rest 
by  simply  ceasing  from  work,  but  there  is  no  complete 
rest,  particularly  for  the  brain,  except  in  sound  sleep. 

The  nature  and  cause  of  sleep  are  not  known  ;  but  it 
is  known  that  during  that  time  the  fatigued  and  shrivelled 
cells  gradually  become  round  and  full,  and  thus  are 
ready  for  vigorous  effort  when  the  period  of  sleep  has 
passed. 

During  sleep  every  organ  of  the  bodj'  partially  or 
completely  suspends  operation.     All  consciousness   and 


TTYCIKXK    OF    TIIK    NKRVOFS    SYSTRM      277 

all  voluntary  action  cease  completely  in  sound  sleep. 
Even  reflex  action  is  slower  in  response  to  any  stimulus. 
Breathing,  beating  of  the  heart,  and  excretion  continue, 
but  at  a  slower  rate. 

Sleep,  then,  is  a  period  of  complete  rest,  during  which 
the  cells  constantly  gain  in  energy-yielding  material,  and 
at  the  same  time  there  is  a  minimum  of  expenditure  of 
energy. 

Amount  of  sleep  necessary. — The  amount  of 
time  that  should  be  spent  in  sleep  varies  with  age,  occu- 
pation, temperament,  and  state  of  health.  Eight  hours 
is  probably  a  fair  average.  Children  need  more  than 
eight  houi-s,  and  old  people  less.  Most  j^eople  take  too 
little  rather  than  too  much  sleep.  This  is  especially 
true  of  active  young  men  and  women.  Xeeded  sleep 
that  is  lost  can  never  be  completely  made  up  at  a  later 
date.  The  over-expenditure  of  energy  is  not  a  matter 
of  much  consequence,  for  energy  is  plentiful  in  the  world  ; 
but  it  is  a  matter  for  most  serious  consideration  that  the 
machine — the  cell  or  organ, — may  therebj^  be  injured  so 
that  its  capacity  for  receiving  and  transmitting  energy  is 
thereafter  lessened. 

Vigorous  mental  exercise  is  conducive  to  strength  of 
intellect.  The  more  the  mind  is  properly  used  the 
stronger  it  becomes,  just  as  a  proper  exercise  of  muscle 
will  result  in  its  development.  But  there  are  limits 
beyond  which  either  brain  or  muscle  will  be  injured  by 
further  exercise.  The  limit  is  reached  when  the  store  of 
energy  runs  low  and  demands  are  made  upon  them  be- 


278  THIED   BOOK   OF   PHYSIOLOGY 

yond  their  ability  to  perform.  At  such  a  time  a  period 
of  complete  rest  in  sleep  must  be  taken,  and  should  be 
continued  until  the  cells  are  again  stored  and  ready  for 
a  period  of  activitj'. 

When  a  youth  is  healthy  and  his  sleep  is  natural,  he 
will  not,  as  a  rule,  sleep  too  long.  A  good  rule  is,  ^' Early 
to  ])ed  and  late  to  rise  (if  necessary),  but  wide  awake 
and  intense  all  day."  Things  are  accomplished  in  this 
world  not  by  long  time  and  weak  effort,  but  by  intense 
application  in  a  short  time.  Only  those  who  take  plenty 
of  sound  sleep  can  have  a  stock  of  energy  sufficient  for 
sustained  effort  during  even  a  short  time. 

A  student  who  si:>ends  enough  time  in  sound  sleep  is 
never  injured  by  the  amount  of  work  expected  of  him  in 
the  schools :  but  one  who  spends  a  night  amid  the  excite- 
ments and  distractions  of  a  social  gathering  and  takes 
only  a  few  hours  of  the  morning  for  a  light  and  fitful 
sleep,  and  ends  up  a  series  of  injuries  with  a  forced  and 
hurried  breakfast,  can  hardh'  be  equipped  for  a  stren- 
uous day's  work.  The  efforts  of  such  an  one  are  attempts 
to  draw  from  a  store  which  is  already  exhausted. 

How  to  induce  sleep. — Under  normal  conditions, 
sleep  is  perfectly  natural  and  easy,  and  nature  will  herself 
determine  the  time  and  the  amount  that  are  necessary. 
But  the  modern  way  of  living  is  producing  an  increasing 
number  of  those  who  suffer  from  insomnia.  The  intense 
activity  of  the  day,  accompanied  by  worry  and  excite- 
ment, the  overtaxed  mind  and  body,  the  stimulation  of 
drugs,  the  unhygienic  forms  of  dress,  the  lack  of  periods 


HYGTENR    OF   TIFF.    NKRVOUS   SYSTKM     279 

of  rt'post'  :iiul  ix'cieatioii,  and  indulgence  in  the  use  of 
alcoliolic  diinks.  and  the  excessive  use  of  tobacco,  all 
tend  to  ])r()duce  a  condition  of  the  body  which  is  apt  to 
result  in  insomnia,  or  at  least  in  very  light  and  restless 
sleeping.  Even  without  any  apparent  fault  of  the  suf- 
ferer, sleep  often  comes  tardily  or  not  at  all. 

Narcotics,  such  as  morphine,  are  often  taken  to  pro- 
duce artificial  sleep,  but  such  a  i^ractice  is  very  danger- 
ous, and  should  be  resoited  to  only  on  the  advice  of  a 
competent  physician. 

Those  who  have  a  difficulty  in  going  to  sleep  may  often 
profit  by  a  few  simple  rules,  as  follows : 

(1)  After  being  dressed  for  the  night,  take  some  light 
gymnastic  exercises  with  dumb-bells,  and  also  by  rising 
slowly  a  number  of  times  upon  the  toes  and  then  upon 
the  heels. 

(2)  Take  a  warm  bath  and  rub  the  body,  thus  re- 
moving any  cutaneous  irritation  ;  or  simply  bathe  the 
feet  and  legs  in  cold  water. 

(3)  See  that  there  is  sufficient  ventilation  to  keep  the 
air  fresh  during  the  night.  Sleep  on  a  fairly  hard  mat- 
tress,— never  on  feathers.     Use  only  light  covers. 

(4)  Do  not  attempt  to  think  out  a  i^roblem  or  make 
any  kind  of  mental  effort  after  retiring.  Get  the  mind 
as  nearly  as  possible  in  a  state  of  inactivity. 

(5)  Make  a  serious  effort  to  dismiss  all  worry  and  ex- 
citement. Keep  the  mind  on  some  pleasant  experience 
or  anticipation.  Do  not  dwell  on  an  imaginary  train  of 
possible  evils. 

(6)  Relax  every  muscle  in  the  body.     This  is  impor- 


280  THIRD   BOOK   OF   PHYSIOLOGY 

taiit.  Even  when  the  body  appears  to  be  in  repose,  it  will 
often  be  found  that  several  muscles  of  the  legs,  arms,  or 
neck  are  tense.  Practise  the  art  of  relaxation  several 
times  each  day,  until  it  can  be  easily  and  completely 
done.  Efficiency  in  the  art  of  complete  relaxation  is 
valuable  not  only  for  the  purpose  of  inviting  sleep,  but 
also  for  periods  of  repose  which  should  be  taken  during 
the  day. 

(7)  Retire  with  the  intention  of  at  once  going  to  sleep, 
and  thus  a  habit  may  be  formed  in  which  sleep  is  asso- 
ciated with  that  environment. 

Good  and  bad  habits. — Habit,  as  already  ex- 
plained, is  a  tendency  to  do  again  in  the  same  way  the 
things  which  have  often  been  done  before.  Habits  may 
be  good  or  bad.  Either  kind  may  become  fixed.  Xo 
one  cares  to  get  rid  of  a  good  habit,  and  fortunately  it 
would  be  difficult  to  do  even  if  one  did  wish  to  change 
it.  Bad  habits  become  equally  fixed  and  difficult  to 
change. 

It  is  necessary  to  any  man's  success  that  he  should  be, 
in  most  things,  a  creature  of  habit,  and,  of  course,  these 
habits  must  be  good  ones.  In  all  things  which  a  man 
does  by  force  of  habit,  he  will,  if  his  habits  are  good,  do 
the  right  thing  in  the  right  way  without  thinking  about 
it.  Herein  is  the  great  advantage  and  economy  of  being 
a  creature  of  correct  habits,  and  nothing  so  handicaps  a 
young  man  or  woman  as  habits  which  are  incorrect. 

Bad  habits  include  more  than  immoral  tendencies.  A 
very  moral  man  often  has  some  bad  habits.     An  awkward 


llV(ilEXE    UV   THE    NEliVOlIS   SYSTEM     281 

walk,  carelessness  in  dross,  impolite  address,  improper 
table  manners,  wrong  forms  of  speech  in  common  con- 
versation, scrawly  and  illegible  writing,  lack  of  intensity 
in  effort,  tendency  to  slight  work,  and  so  on,  are  all 
habits  which  will  remain  and  grow  more  and  more 
marked,  unless  they  can  be  forcibly  corrected.  No  edu- 
cation is  more  valuable  to  a  man  or  woman  than  the 
numerous  good  habits  which  may  be  formed  in  the  earlier 
years  of  life,  for,  in  its*  broadest  sense,  habit  is  only 
another  name  for  character. 

In  earl}^  life  the  nervous  system  is  in  its  plastic  stage. 
Habits  are  then  easily  formed  or  changed.  But  every 
act,  every  thouglit,  and  every  way  of  doing  things  make 
a  lasting  impression  even  on  the  youthful  mind.  At  the 
age  of  twenty-five  or  thirty  years  the  nervous  tissue  may 
be  said  to  have  become  set.  Only  by  a  strong  effort  of 
the  will  and  by  continued  practice  can  a  habit  hitherto 
formed  be  now  changed,  and  it  is  doubtful  that  a  radical 
change  can  ever  be  made. 

The  nervous  system,  however,  never  entirely  loses  its 
plastic  nature.  By  persistent  effort  old  habits  may  be 
practically  changed,  though  the  tendency  to  return  to  the 
old  habit  is  always  imminent. 

These  considerations  make  the  education  of  the  youth 
of  to-day  a  matter  of  supreme  importance  for  the  sake 
of  the  coming  generation. 

Effect  of  alcohol  on  the  nervous  system.— 
The  nervous  system,  more  than  any  other  part  of  the 
body,  is  injured  by  the  use  of  alcohol.     The  same  amount 


282  THlIiD    BOOK   OF    PHYSIOLOGY 

of.  injury  to  the  braiu  will  have  a  greater  evil  effect, 
because  the  brain  is  the  controlling  organ. 

An  injury  to  the  head  of  any  organization  is  more 
serious,  as  far  as  the  welfare  of  the  organization  is  con- 
cerned, than  a  similar  injury  to  an  inferior  member. 

We  have  shown  that  a  centre  in  the  medulla  controls 
the  rate  of  the  heart-beat.  Any  injury  to  this  centre 
will,  of  course,  affect  the  action  of  the  heart,  though  the 
heart  itself  may  be  perfectly  sound.  In  a  similar  manner 
whatever  affects  the  vasomotor  nerve-centres  will  modify 
the  circulation  of  the  blood,  and  any  injury  to  a  motor 
area  of  the  cerebral  cortex  will  affect  its  control  of  the 
muscles  which  it  stimulates  to  action.  The  cause  of 
dyspepsia  may  lie  in  the  nerve-centre  which  normally 
stimulates  the  secretion  of  the  gastric  glands. 

Thus  alcohol  works  a  double  evil  in  that  it  injures  the 
various  organs  in  ways  already  explained,  and,  worst  of 
all,  it  weakens  or  finally  destroys  the  nervous  centres 
upon  which  the  other  organs  must  rely  for  stimulation, 
nutrition,  and  recovery  from  iujurj-. 

Mankind  has  had  a  long  experience  with  alcohol,  and 
many  scientific  investigations  have  been  made  as  to  its 
effects  on  the  human  system.  Almost  without  exception 
its  continued  use  as  a  drink  has  been  found  to  have  an 
evil  effect.  Whether  the  matter  is  considered  from  a 
physiological,  a  financial,  or  a  moral  stand-point,  the  use 
of  alcoholic  drinks  as  a  beverage  is  condemned  by  scien- 
tific facts  as  well  as  by  the  experience  of  mankind.  The 
so-called  arguments  in  its  favor  are  chiefly  apologies  for 
its  continuance,  and  tjie  main  motive  back  of  the  traffic 


IIVCIKNE    or    TIIK    NKIiA^OUS    SYSTEM     28;{ 

ill  intoxiciitin<;  li({iiors  is  the;  soiirci;  of  gain  to  its  pro- 
moters. 

Alcohol  holds  iiii  important  place  in  the  arts,  and  it 
may  be  useful  jls  a  fuel,  but  it  is  every  day  becoming 
more  evident  that  alcoholic  beverages,  even  in  moderate 
quantities,  are  evil,  and  only  an  evil. 

Alcohol  in  small  doses.— There  has  been,  and  is 
now,  a  prevalent  notion  'that  if  alcoholic  liquors  are  used 
in  moderate  quantity,  much  good  may  be  derived  from 
them,  or  at  least  no  injury  would  be  done. 

This  mistaken  notion  is  the  chief  cause  of  both  the 
moderate  and  the  immoderate  drinking  of  alcohol. 

The  masses  of  people  do  not  have  the  facilities  or  the 
inclination  to  investigate  the  subject ;  and  because  they 
know  that  a  moderate  use  of  malted  liquors  produces  no 
apparent  evil,  while  it  does  often  bring  about  a  feeling  of 
bodily  comfort  and  of  mental  cheer,  they  are  easily  de- 
ceived. 

The  body  has  within  itself  wonderful  agencies  of  re- 
cuperation. It  differs  from  any  other  machine  in  that  it 
can  build  uj)  and  repair  itself.  Whenever  any  injurious 
substance,  as  alcohol,  is  taken  into  the  body,  an  effort  is 
at  once  made  to  excrete  it ;  but  before  this  can  be  done 
much  of  it  is  carried  in  the  current  of  blood  to  the  various 
tissues,  where  it  exerts  its  poisonous  effect  upon  the  pro- 
toplasm of  the  cells — particularly  the  nerv^e-cells.  If  the 
amount  of  alcohol  is  small  and  is  much  diluted,  the  in- 
jury to  the  cells  may  be  slight  and  easil}^  repaired.  It 
should  be  carefully  noted,  however,  that  alcohol,  in  what- 


284  THIRD   BOOK   OF   PHYSIOLOGY 

ever  doses,  presents  itself  to  the  cells  as  an  enemy,  whose 
evil  effects  are  to  be  either  prevented  or  repaired. 

Because  the  cells  are  able  to  survive  the  effects  of  a 
small  dose  is  no  proof  that  it  is  not  a  poison,  any  more 
than  small  doses  of  arsenic  or  strychnine  might  be  con- 
sidered harmless  because  they  do  not  at  once  destroy  the 
tissues  or  arrest  the  functions  of  the  organs.  Food,  on 
the  other  hand,  comes  to  the  cells  without  any  antago- 
nism, and  is  assimilated  in  a  natural  manner. 

These  facts  are  of  the  greatest  importance  in  the  con- 
sideration of  this  subject,  for  the  apparent  immunity  from 
the  evil  effects  of  the  small  dose  is  the  gateway  through 
which  all  immoderate  drinking  steadily  creeps  in. 

This  immunity,  however,  is  only  apparent.  Each 
recovery  from  the  poisonous  effects  leaves  the  nervous 
system  with  less  ability  to  resist  the  next.  Its  evil  effects 
are  thus  cumulative,  and  sooner  or  later  become  apparent 
in  a  weakened  condition  of  some  organ  or  a  suspension 
of  some  function. 

Most  people  do  not  look  far  into  the  future  or  are 
willing  to  take  chances.  Unless  serious  pain  or  sickness 
follows  at  once  upon  a  certain  line  of  conduct,  they  are  apt 
to  continue  in  a  course  which  gives  present  gratification. 
As  a  consequence,  the  evils  from  moderate  drinking  are 
most  insidious  in  character,  for  irreparable  harm  may  be 
done  before  the  drinker  is  aware  of  his  condition. 

Alcohol  as  a  mental  stimulus. — The  first  effect 
of  a  drink  of  alcoholic  liquor  is  an  apparent  stimulation 
of  the  nerve-centres  to  greater  activity.     This  has  led 


TTYGTKNE    OF    THE    XERVOUS   SYSTP:M     285 

manj'  to  believe  that  alcohol  has  the  effect  of  rousing 
mental  activity,  and  that  one  can  write  and  think  more 
brilliantly  under  such  a  stimulus.  But  careful  examina- 
tion will  show  that  alcohol  produces  in  the  brain  a  con- 
dition of  excitement  i-ather  than  that  of  healtlifnl  stimula- 
tion. It  may  properly  be  compared  to  the  introduction 
of  a  poisonous  serpent  into  the  midst  of  a  company  of 
people  in  an  enclasure  from  which  they  cannot  escape. 
There  would  no  doubt  be  intense  activity  in  the  com- 
pany, and  great  excitement,  but  the  motive  in  all  their 
efforts  would  be  that  of  self-preservation. 

It  would  not  be  probable  that  this  increased  activity 
would  result  in  any  worthy  accomplishment,  and  after 
the  serpent  is  removed  it  is  quite  x»robable  that  each 
member  of  the  company  would  find  himself  in  a  state 
of  fatigue,  which  would  prevent  any,  even  natural,  effort 
until  after  a  period  of  rest. 

WTien  one's  brain  is  thrown  into  a  state  of  excitement 
by  alcohol,  he  gets  an  exaggerated  idea  of  his  capacity  to 
think  and  work.  He  imagines  he  is  doing  more  than  he 
is  in  fact.  One  who  writes  a  production  in  this  state  of 
excitement  may  at  the  time  be  highly  j)leased  with  his 
effort,  but  a  calm  review  later  will  show  that  he  greatly 
overestimated  his  work. 

A  hearty  meal  of  good  food,  abundance  of  fi-esh  air, 
and  plenty  of  sleep  are  the  natural  and  proper  provisions 
for  intense  and  sustained  effort. 

Immoderate  use  of  alcohol. — Every  one  abhors 
the  coiidition  uf  a  confirmed  drunkard,  but  nearly  every 


286  THIED   BOOK   OF   PHYSIOLOGY 

one  who  drinks  immoderately  was  at  one  time  only  a  mod- 
erate drinker.  Immoderate  drinking  is  a  natural  result 
of  moderate  drinking.  Under  the  continuous  poisonous 
effects  of  alcohol,  even  in  moderate  doses,  the  nervous  tis- 
sue deteriorates  and  loses  its  former  delicacy  of  response  to 
stimuli.  More  alcohol  must  now  be  taken  to  produce  the 
desired  effect.  Besides,  an  appetie  for  alcohol  is  gradu- 
ally contracted,  and  becomes  so  strong  that  all  the  efforts 
of  the  better  side  of  a  man's  nature  cannot  resist  it. 
The  antidote  for  alcoholic  poison  is  more  alcohol.  Con- 
siderations of  home,  family,  morals,  and  respect  of  others 
gradually  come  to  count  for  naught.  Such  an  one  is 
suffering  from  a  self-inflicted  disease  which  is  known  as 
dipsomania, — madness  for  drink. 

The  disease  may  yield  to  j^roper  treatment  and  the 
patient  may  again  get  control  of  himself,  but  he  never 
fully  recovers,  and  a  very  slight  temj^tation  will  in  most 
cases  lead  him  again  into  inebriety. 

Complete  recovery  from  the  effects  of  immoderate  and 
long- continued  use  of  alcohol  is  imi)ossible  because  of 
the  changes  made  in  the  character  of  the  nervous  tissue. 
It  is  found  that  the  brain  becomes  shrunken  in  size  and 
the  space  about  it  becomes  filled  with  water.  Many  of 
the  cells  degenerate  into  fat  or  connective  tissue.  Thus 
the  essential  and  vital  part  of  the  tissue  is  sacrificed,  and 
of  course  the  power  to  think  and  control  the  body  is 
^proportionately  reduced. 

The  last  stage  of  dipsomania  is  often  delirium  tremens. 
This  is  the  most  horrible  condition  to  which  a  human 
being  can  be  reduced,   and  may  come  on  at  any  time 


]TV(;iKNK    OF   'niK    XKI{Vr)rs    SVSTKM      287 

iluriiig  a  period  of  drinkinjjj, — even  early  in  the  career  of 
the  drnnkard.  Il  in  ('IVect  transforms  a  man  into  a  wild 
lM*ast.  Tlu'  iimscles  are  all  in  a  tremoi-.  becanse  the 
poisoned  motor  centres  can  no  longer  control  tliem. 
Tli«'  mind  is  delirious  and  imagines  all  sorts  of  horrible 
iH'asts,  serpents,  and  insects,  which  are  ever  in  pursuit 
and  cannot  be  driven  away.  Death  may  come  to  the 
sutierers  relief  at  any  instant,  or  the  tx)rture  may  hust  for 
several  days,  and  then  be  followed  by  a  return  of  the 
rational  state. 

Hereditary  effect. — Nothing  in  physiology  is  more 
clearly  established  than  the  fact  that  children  inherit 
traits,  dispositions,  bodily  and  mental  strength  or  weak- 
ness from  their  parents. 

Children  of  drunken  parents  are  often  at  a  great  disad- 
vantage because  of  some  inherited  weakness.  Defects 
of  some  kind  are  usually  handed  down  from  a  father  or 
grandfather  who  has  been  given  to  the  use  of  alcoholic 
drinks.  Maybe  the  child  will  have  weak  lungs  and  be 
predisposed  to  consumption.  Maybe  there  will  be  some 
physical  defect  in  the  brain,  with  a  consequent  dulness 
or  tendencj^  to  insanity.  The  general  tone  of  both  mind 
and  body  may  be  inferior,  and  the  child  be  thus  handi- 
capped for  life. 

An  appetite  for  strong  drink  frequently  appears  in  the 
children  of  drinking  parents.  Such  an  appetite  may  be 
aroused  by  a  few  drinks  of  alcohol.  Thus,  one  who  per- 
sists in  drinking  alcohol  injures  not  only  himself  but 
also  all  those  dependent  upon  him  while  he  lives,  and 


288  THIRD   BOOK    OF  PHYSIOLOGY 

may  transmit  the  evil  effects  of  liis  course  to  generations 
that  follow. 

The  only  safe  course. — There  is  only  one  safe 
course  in  regard  to  the  use  of  alcoholic  liquors,  and  that 
is  totally  to  abstain  from  their  use.  An  occasional  indul- 
gence in  some  mild  alcoholic  drink  may  do  no  perma- 
nent injury  that  is  apparent ;  for,  as  we  have  explained, 
the  body  is  able,  within  certain  limits,  to  repair  any 
organ  that  is  injured.  But  whatever  may  be  said  about 
the  harmlessness  of  the  small  dose  of  alcohol,  it  is  still  in 
accordance  with  the  testimony  of  the  best  experts  and  of 
the  best  elements  of  the  human  race  that  the  only  safe 
course  is  total  abstinence. 

The  experience  of  men  in  the  future  will  be  just  as  it 
has  been  in  the,  past ;  and  the  testimony  of  individuals, 
communities,  and  nations  in  the  past  is  all  against  the 
use  of  alcohol  as  a  beverage. 

Tobacco  and  the  nervous  system. — Many  of 
the  fundamental  objections  to  the  use  of  alcohol  can  also 
be  urged  against  the  use  of  tobacco.  Tobacco  contains  a 
violent  i^oison  called  nicotine.  A  very  small  quantity 
of  this  poison  in  a  concentrated  form  would  soon  cause 
death.  When  by  any  use  of  tobacco  it  is  introduced 
into  the  current  of  blood,  it  of  course  is  carried  to  the 
brain  as  well  as  to  other  parts  of  the  body. 

Its  general  effect  upon  the  nerve-cells  is  much  the  same 
as  that  of  alcohol.  That  is,  it  tends  to  do  injury,  and 
must  be  either  warded  off  or  the  injury  nuist  be  repaired. 


HYGIENE    OF   TIIF.    XERVOUS   RVSTFM     289 

^\  hen  Olio  hjus  attained  liii^  full  growth,  is  healthy,  and 
is  engaged  actively  in  some  outdoor  work,  the  noticeable 
l)hysical  injury  from  tlio  moderate  use  of  tobacco  may 
not  be  easily  recognized.  To  students,  clerks,  or  any 
whose  constitutions  are  delicate,  and  whose  work  is  in 
close  rooms,  the  use  of  tobacco  is  very  harmful.  This  is 
particularly  true  of  the  cigarette.  Many  investigations 
have  been  made  in  regard  to  the  smoking  habit  among 
students  in  college,  and  every  report  of  such  investiga- 
tion shows  that  the  smoker  is  inferior  in  his  standing. 

The  worst  effect  of  tobacco  is  found  in  its  use  by  the 
young.  Those  who  are  growing  are  likely  to  stunt  their 
growth  by  the  use  of  tobacco.  Nicotine  will  seriously 
affect  certain  nervous  centres,  thereby  causing  organic 
troubles,  such  as  the  irregular  action  and  palpitation  of 
the  heart  so  common  with  those  who  use  tobacco  freely 
or  with  the  youth  who  uses  tobacco  at  all.  Other  nerve- 
centres  wdiich  regulate  secretion  and  excretion  are  also 
injured,  so  that  blood  improperly  purified  is  distributed 
to  the  various  cells.  The  easily  fatigued  muscle  of  the 
smoker  is  an  evidence  of  this  fact. 

Worst  of  all,  the  mental  powers  are  weakened.  This 
results  both  from  the  poisoning  of  the  brain-cell  itself,  and 
also  from  the  fact  that  the  other  organs  do  not  furnish 
pure  blood  for  its  nourishment.  It  will  be  observ^ed  in  the 
public  schools  that  the  youth  who  smokes  (if  he  smokes 
at  all  he  will  usually  smoke  a  great  deal)  will  be  restless 
and  inattentive,  will  lack  ability  to  appl}^  himself  and 
hold  his  mind  to  his  studies,  and  of  course  will  fall  be- 
hind and  want  to  quit  school.     It  is  also  observed  that 

19 


290  THIED   BOOK    OF   PHYSIOLOGY 

students  who  are  in  college  and  wlio  are  habitual  smokers 
cannot  with  credit  meet  the  requirement  in  those  studies 
which  can  be  mastered  only  by  concentrated  effort  and 
attention.  This  statement  can  be  ^'e^ified  by  college 
statistics  on  this  point. 

Cigarette  smoking  is  the  most  injurious  use  of  tobacco 
for  the  reasons  already  given  under  the  subject  of  respi- 
ration. 

Opium. — Opium  is  a  powerful  narcotic  poison.  Its 
use  is  not  so  common  in  the  United  States  as  is  that  of 
alcohol  and  tobacco,  but  it  is  all  too  common.  The  vic- 
tims of  the  opium  habit  yield  to  an  appetite  which  they 
are  helpless  to  resist,  and  sink  to  extreme  degradation  of 
both  mind  and  body.  The  druggists  of  almost  every 
town  can  point  out  a  number  of  both  men  and  women 
who  will  resort  to  any  deception  to  secure  opium.  They 
will  lie  or  steal,  if  necessary,  to  secure  the  money  to  l)uy 
the  drug.  The  victims  are  stealthy  in  their  practice,  and 
will  usually  deny  that  they  use  it,  so  that  the  prevalence 
of  the  habit  is  not  commonly  known. 

The  opium  habit  is  easily  contracted.  Morphine  is  a 
tincture  of  opium  and  is  frequently  used  to  allay  pain. 
Its  continued  use  may  engender  in  the  system  a  craving 
for  it  which  is  difficult  to  resist. 

Some  patent  medicines,  which  are  advertised  as  '^pain- 
killers" and  "stomach  bitters,"  contain  as  much  as  40 
per  cent,  or  more  of  alcohol  and  often  a  considerable  quan- 
tity of  morphine.  Both  drugs  are  narcotics,  and  of 
course  will  stop  pain  by  x^aralyzing  the  sensory  nerves. 


IIV(rIENR   OF   TIH^:    NRIiVOlTS   SYSTIvM     2:il 

In  such  ways  the  unsuspecting  victim  may  after  a  time 
find  liimself  a  slave  to  the  opium  liabil,  from  wliicli  it  is 
very  jn'obable  he  Mill  nevei-  l)e  ri<M'. 

QUESTIONS   FOR   REVIEW. 

1.  Why  is  blood  distributed  to  tiie  nervous  system  ? 

2.  What  connection  is  there  between  food  and  nervous  opera- 
tions ? 

3.  Show  how  tlie  brain  is  the  favored  organ  of  the  })ody.     Why 
is  this  po  ? 

4.  How  can  we  supply  the  brain  with  healthful  food  ? 

5.  How  i.s  blood  conducted  to  the  brain  ? 

6.  Explain  wliy  brain-cells  become  fatigued. 

7.  How  does  a  fatigued  cell  differ  from  a  rested  one? 

8.  AVhat  is  the  condition  of  the  body  and  mind  during  sleep  ? 

9.  What  is  the  purpose  of  sleep? 

10.  How  much  sleep  is  necessary? 

11.  Will  study  injure  the  mind  ?     AVhat  will  ? 

12.  What  is  insomnia?    What  causes  it  ? 

13.  Ciive  some  good  ways  of  inducing  sleep. 

14.  What  is  meant  by  repose  and  relaxation  ? 

15.  In  a  broad  sense,  what  is  meant  by  good  and  bad  habits  ? 

16.  What  is  the  best  time  of  life  for  the  formation  of  habits? 
Why  ? 

17.  Why  is  an  injury  to  the  brain  more  serious  than  an  injury  to 
other  organs  ? 

18.  How  does  injury  to  the  brain  work  a  double  evil  ? 

19.  Tell  all  you  can  about  the  use  of  alcohol  in  small  doses. 

20.  Is  alcohol  beneficial  as  a  stimulus  to  mental  activity?     Ex- 
plain. 

21.  What  is  the  best  condition  of  the  brain  for  clear  and  strong 
thinking? 

22.  Describe  dipsomania. 

23.  What  is  the  hereditary  effect  of  excessive  drinking? 


292  THIRD   BOOK   OF   PHYSIOLOGY 

24.  What  is   the   only  safe   course   in  reference  to  the   use   of 
alcohol  ? 

25.  Describe  the  effects  of  tobacco  on  the  nervous  system. 

26.  Tell  all  you  can  about  the  opium  habit. 

27.  What  is  opium,  and  where  is  it  produced?     (See  dictionary 
and  cyclopaedia. ) 


oil  A  1'  TKK    X  \   I  I  I 

Tin:    SIMlCI.Vr.    SENSES 

What  the  special  senses  are.— The  special  senses 
art-  tiH>S('  whirli  arc  prodiUMMl  by  special  organs  at  the 
oiiliT  ends  of  sensory  nerves.  They  are  seeing,  hearing, 
toiiehing,  tasting,  and  smelling.  Tlie  special  organs  which 
piodncc  these  sensiitions  are  the  eyes,  the  ears,  the  touch 
corpnseles,  and  tlio  special  endings  of  the  gustatorg  and 
olfactorij  nerves. 

General  sensations.— There  are  many  other  sensa- 
ti(tus  ill  the  body  which  may.  more  properly,  be  classed 
as  general  sensations.     These  are  such  as 

(1)  'Vhid  sense  of  temperature,  which  is  located  principally 
in  Ihe  skin.  By  this  sense  we  are  promptly  informed  as 
to  whether  the  temperature  is  too  high  or  too  low  for  the 
most  successful  operation  of  the  cells  and  organs  which 
are  affected.  This  sense  is  also  acute  in  the  mouth  and 
at  the  entrance  of  the  nose.  These  are  the  points  of 
entrance  of  food  and  air,  and.  as  we  might  expect,  we 
find  here  several  outposts,  or  guards,  such  as  touch,  taste, 
smell,  and  this  additional  one. — the  sense  of  temperature. 

(2)  The  sense  of  pain.  Wiien  any  sensory  nerve  is  in- 
jured or  is  excited  beyond  what  is  natural,  a  sense  of 
pain  results.  When  the  epidermis  is  removed  from  any 
part,  as  in  case  of  a  blister  on  the  finger,  contact  with 

293 


294  THIED   BOOK   OF   PHYSIOLOGY 

the  exposed  true  skin  will  produce  pain  rather  than  a 
sense  of  touch.  ^Vhile  pain  is  sometimes  considered  a 
great  evil,  yet  it  is  in  fact  a  very  great  blessing,  for 
otherwise  we  would  become  verj-  careless  in  regard  to 
the  liealth  of  our  bodies.  Even  if  we  always  tried  to  do 
what  was  best,  we  would  often  be  ignorant  of  the  effects 
of  our  course  except  as  we  were  checked  by  pain.  The 
cause  of  pain,  and  not  the  pain  itself,  is  the  thing  to  be 
avoided. 

(3)  Sense  of  hunger,  thirst,  fatigue,  or  illness  are  all  gen- 
eral senses  which  are  very  vague  in  their  character. 
They  cannot  be  definitely  located,  and  aie  probably  the 
combined  result  of  sensory  impulses  from  all  or  many 
cells  of  the  body.  Their  purpose  is  to  inform  the  cere- 
brum as  to  the  state  of  the  cells  in  reference  to  their 
ability  to  perform  their  natural  functions. 

(4)  The  sense  of  weight.  By  this  sense  it  is  possible  to 
determine  the  weight  or  resistance  of  an  object  by  the 
amount  of  muscular  exertion.  This  sense  ms-v  be  so 
trained  that  it  becomes  fairly  reliable. 

(5)  The  sense  of  pressure.  This  sense  is  most  delicate 
on  the  forehead,  where  a  slight  increase  or  decrease  of 
pressure  may  be  detected. 

Advantage  of  the  special  senses.— By  means  of 
the  special  senses  we  are  able  to  gain  elearhj  defined 
knowledge  of  objects  outside  the  body.  If  the  fine 
branches  of  the  optic  nerve  were  distributed  in  the  skin 
of  the  face,  we  could  probably  tell  darkness  from  day- 
light, but  could  never  have  distinct  images  of  objects 


THK   SPECIAL    SKXSp:S  295 

such  as  we  ^a't  when  light  tirst  passes  tliruugh  the  eye 
and  then  falls  upon  the  nerve-ends.  Simihirly,  wo  might 
get  an  idea  of  some  intense  sounds  without  ears.  l>ut  the 
sensation  would  lack  all  distinctness  and  delicacy. 

The  five  special  senses  are  the  five  great  avenues 
through  which  all,  or  nearly  all.  our  knowledge  is  gained. 
It  is  through  them  that  connection  is  made  between  the 
outside  world  and  the  central  nervous  system.  If  all 
sensiitions  were  suddenly  4x)  cease,  a  man  would  continue 
to  live,  but  it  would  be  impossible  for  him  to  determine 
whether  he  existed  or  nut.  He  would  for  a  time  con- 
tinue to  think  as  a  result  of  his  store  of  previous  sensa- 
tions, but  soon  these  would  fade  away,  and  his  mind 
would  become  a  complete  blank.  Thus  we  are  in  constant 
dependence  upon  the  streams  of  sensation  from  our 
special  sense  organs. 

The  two  great  media. — Every  minute  of  our  lives 
we  must  V)e  surrounded  l)y  two  great  media, — the  air  and 
the  ether.  We  might  expect,  then,  to  find,  as  we  do  find, 
that  two  of  the  most  valuable  and  delicate  sense  organs 
are  the  ones  which  record  any  disturbance  in  these  media, 
— the  ear  being  a  receiver  for  waves  of  air,  and  the  eyes 
for  waves  of  ether. 

The  ether  fills  all  space  and  permeates  all  matter. 
When  it  is  agitated  at  any  point,  waves  pass  out  in  every 
direction,  like  the  waves  which  go  out  from  the  point 
where  a  stone  is  thrown  into  a  still  pond,  only  the  ether 
waves  will  go  out  in  all  directions  as  radiations  from  the 
centre  of  a  sphere.     The  sun  is  constantly  sending  out 


296  THIRD   BOOK   OF   PHYSIOLOGY 

waves  of  this  kind,  and  they  travel  the  whole  distance — 
about  93,000,000  miles — from  the  sun  to  the  earth  in 
eight  minutes.  Thus  the  earth  is  flooded  with  waves 
which  cause  nearly  all  the  light  and  heat  we  have  on 
earth.  In  the  same  manner  light  comes  to  us  from  the 
stars,  which  are  vastly  farther  away  than  the  sun.  Thus 
the  eye,  more  than  any  other  sense,  gives  us  knowledge 
of  objects  at  a  great  distance  from  the  body.  The  re- 
gion from  which  we  could  gain  knowledge  would  be 
very  limited  without  this  sense. 

The  air  also  constantly  presses  about  us,  and  any 
vibrating  body  will  start  in  it  a  series  of  waves  that  will 
travel  out  in  all  directions.  These  waves,  however,  con- 
sist of  alternate  condensations  and  rarefactions  of  air, 
while  the  ether  waves  are  simple  undulations.  The  air 
waves  travel  only  about  1100  feet  in  one  second  and  can- 
not go  very  far,  but  probably  fully  as  much  information 
is  brought  to  us  on  air  waves  as  on  the  ether  waves. 

Thus  the  eye  and  the  ear  are  our  two  great  sense 
organs,  because  they  are  made  to  receive  the  vibrations 
which  are  constantly  brought  to  us  on  these  two  great 
and  ever-present  media. 

THE    EYE 

General  anatomy  of  the  eye.— The  eye  is  nearly 
spherical  in  shape,  is  nearly  one  inch  in  diameter,  and  is 
set  in  a  bony  socket  upon  a  bed  of  fat.  Its  principal 
parts  may  be  seen  in  the  cross-section  shown  in  Fig.  126. 
On  the  outside  is  the  sclerotic  coat,  which  on  the  front 
of  the  eye  is  transparent  and   bulges  forward,  forming 


Tin:   SPKCIAL   SENSES 


297 


the  coiiwn.  Just  back  of  the  cornea  is  a  cavity  filled 
with  a  watery  lluid  called  the  aqueous  humor.  Across 
the  rear  part  of  this  chamber  is  stretched  a  curtaiu  called 
the  iris,  through  the  centre  of  which  is  a  round  opening 
called  the  jrupil.  Just  back  of  the  iris  is  the  crysUdlinr 
Jem,  resting  in  a  concave  depression  of  tlie  vitreous  humor, 
which  fills  the  large  central  chamber  of  the  eyeball. 
Next  within  the  sclerotic  coat  is  the  dark-brown  choroid 


Fig.  120. — Cross-section  of  the  eye.  C,  the  cornea;  A^  aqueous 
humor;  /,  iris;  Z/,  cr3"stalline  lens;  F,  vitreous  humor;  .S",  sclerotic 
coat;    CV(,  choroid  coat:   R.  retina;    O,  optic  nerve;    Y^  yellow  spot. 


coat,  which  is  continuous  in  front  with  the  iris.  The 
inner  coat  is  the  retirm.  The  optic  nerve  enters  the  eye  a 
little  below  and  to  the  inner  side  of  the  ball,  and  its 
numerous  branches  are  distributed  to  the  retina.  On 
the  retina,  in  the  centre  of  the  back  part  of  the  ball,  is  a 
spot  about  one  twenty- fourth  of  an  inch  in  diameter.  It 
is  yellow  in  color,  and  so  is  called  the  yellow  spot.  This 
spot  is  in  line  with  the  axis  through  the  cornea  and  the 
crystalline  lens. 


298  THIRD   BOOK   OF   PHYSIOLOGY 

The  purpose  and  operation  of  the  anterior 

parts. — The  function  of  the  cornea,  iris,  and  crystalline 
lens,  all  ^rorking  together,  is  to  produce  a  small  but 
distinct  image  and  locate  it  exactly  on  the  jellow  spot 
of  the  retina.  The  cornea  is  fixed  in  position.  l)ut  the 
iris  will  change  the  size  of  the  pupil  in  accordance  with 
the  brightness  of  the  light,  and  the  lens  will  change  its 
shape  in  accordance  with  the  distance  of  the  object.  The 
cornea  produces  the  image,  the  iris  regulates  the  amount 
of  light,  and  the  lens  locates  the  image  upon  the  yellow 
spot. 

The  cornea. — The  cornea  is  the  transparent  part  of 
the  sclerotic  coat.  It  is  much  more  convex  than  the 
remainintr  surface  of  the  eyeball,  and  is  set  into  the  re- 
maiuing  j^ortion  of  the  sclerotic  coat  much  as  a  crystal 
is  set  into  the  case  of  a  watch.  The  distance  across  the 
cornea  is  about  one-sixth  the  circumference  of  the  ball. 
In  the  normal  eye  the  cornea  has  the  shape  of  a  segment 
of  a  sphere,  its  curvature  being  the  same  in  all  directions. 
The  curvature  is  greatest  in  youth  and  becomes  less  and 
less  iis  age  advances. 

The  function  of  the  cornea  is  to  receive  the  rays  of 
light  which  come  to  it  from  a  point  outside  the  eye,  and 
bend  them  so  that  they  will  meet  again  at  a  point  within 
the  eye.  This  is  done  in  accordance  with  a  principle  in 
light  called  refraction. 

Refraction  of  light. — Whenever  a  ray  of  light 
passes  obliquely  from  one  medium  to  another  of  different 
density  it  will  be  bent  out  of  its  course.     This  is  called 


tup:  siM^ciAL  sf.nses 


209 


rt'fraction  of  light.  In  Fij^.  Vl~,  A,  :i  ray  of  liglitfroin  O 
enters  ohliciuely  into  a  piece  of  glass.  That  is,  it  goes 
from  a  light  incdiinn.  Ilicair.  into  a  dense  modiiim.  tlie 
glitss.      In  that  Ciuse  the  ray  is  always  bent  towards  the 


G 

^'^ 

7?"^ 

^^ 

.1 

\       ^' 

A 


Fio.  yi~. — In  A^  a  ray  starts  from  0,  in  air,  and  enters  plate  «>f 
glass,  G.     RU  the  direction  of  refracted  ray. 

In  i?,  the  rays  from  0  are  refracted  by  lens  L  and  brought  to  point 
F. 


perpendicular,  7*  P.  In  case  the  light  would  start  in  the 
glass,  as  at  T,  then  the  ray,  T  A^  on  going  out  into  a 
lighter  medium,  the  air,  would  be  bent  away  from  the 
perpendicular,  P  P,  and  would  go  to  0. 

Xow.  if  we  take  a  lens  in  the  shape  of  the  cornea,  as 
in  127,  -B,  and  applj'  these  laws  of  refraction,  it  will  be 


300 


THIED   BOOK    OF   PHYSIOLOGY 


plain  tliat  the  rays  of  light  from  0  will  be  V)ent  so  that 
they  will  come  together  at  F. 

Thus,  as  shown  in  Fig.  128.  if  an  arrow,  O.  l)e  the  ob- 
ject, then  rays  of  light  from  any  point  of  the  arrow  will, 


Fig.  128. — Eays  <>f  light  from  each  end  of  the  arrow,  0,  are  brought 

to  a  focus  at  I. 


after  passing  through  the  cornea,  be  bent  so  that  they 
will  come  together  again,  and  form  an  image  of  that 
point.  In  the  figure  only  two  rays  are  drawn  from  each 
end  of  the  arrow,  as  that  is  all  that  is  needed  to  find  the 
two  ends  of  the  image.  The  image  of  other  points  of 
the  arrow  will  lie  between  the  two  ends.  It  is  observed 
that  the  image  is  inverted,  and  that  is  the  i^osition  of  all 
images  in  the  eye.  The  cornea  alone  will  produce  a 
distinct  image,  but  it  cannot  produce  satisfactory  vision 
without  the  aid  of  the  iris  and  crystalline  lens,  as  will 
now  be  explained. 

The  iris. — Iris  in  mythology  was  the  goddess  of  the 
rainbow,  and  hence  the  name  of  this  curtain  with  its 
variety  of  color.  The  iris  is  the  chief  source  of  the 
beauty  of  the  eye,  but  nature  intended  it  for  a  useful 
purpose  in  vision.  In  the  iris  are  two  sets  of  muscle- 
fibres.     One  kind  radiates  from  the  pupil  to  the   outer 


TIIK   SPECIAL    SKNSES 


301 


edge  of  the  iris.  When  these  contract  they  pnll  the  iris 
away  from  tlie  centre  in  all  directions,  thus  making  the 
pupil  larger.  In  the  other  set  the  fibres  are  concentric 
about  the  pupil,  and  when  they  contract  the  iris  is  drawn 
towards  the  centre,  and  thus  the  pupil  is  made  smaller. 
The  action  is  automatic,  a  bright  light  causing  a  contrac- 
tion of  the  concentric  fibres  and  so  a  smaller  pupil,  and 
a  dull  light  permitting  the  iris  to  be  drawn  back  and  so 
a  larger  pupil. 

The  purpose  of  this  arrangement  is  twofold  :    (1)  To 
produce  on  the  retina  an  image  of  the  Siime  brilliancy, 


Fig.  129. — Diagram  illustraring  the  aberration  of  focus  caused  by  a 
spherical  lens.  0,  origin  of  light ;  F,  focus  where  the  five  rays 
through  the  central  part  of  the  lens  meet ;  a,  a,  the  rays  which  pass 
through  outer  edge  of  lens  and  are  focused  at  .S";  T,  T,  is  a  screen  cor- 
responding to  the  iris  in  the  eye.  It  shuts  off  all  rays  except  those 
which  pass  most  nearly  through  the  centre  of  the  lens. 

whatever  be  the  intensity  of  the  source  of  light.  Vision 
would  be  dimmed  by  too  much  as  well  as  by  too  little 
light,  and  too  bright  an  image  would  injure  the  retina, 
(2)  To  shut  out  the  rays  which  would  otitierwise  pass  in 
through  the  edges  of  the  cornea  and  crystalline  lens  and 


302  THIRD    BOOK   OF   PHYSIOLOGY 

would  not  come  to  a  focus  at  the  same  point  as  the  other 
rays,  which  entered  near  the  centre  of  the  cornea.  This 
is  illustrated  in  Fig.  129.  The  value  of  the  iris  in  this 
respect  is  experienced  by  those  who  have  belladonna 
placed  in  the  eye  to  cause  the  pupil  to  expand  so  that 
the  interior  of  the  eye  can  be  examined.  Clear  vision  is 
impossible  until  the  effect  of  the  belladonna  has  passed 
away. 

In  many  optical  instruments  a  screen  with  a  round 
hole  through  the  centre  is  placed  in  front  of  the  lens  to 
secure  a  distinct  image  according  to  the  principles  just 
explained. 

The  crystalline  lens. — The  crystalline  lens  is  a 
transparent  colorless  body  in  the  shape  of  a  double  con- 
vex lens.  It  is  about  one-third  of  an  inch  broad  and 
one-sixth  of  an  inch  through  its  thickest  part.  On  its 
anterior  side  it  is  bathed  with  the  aqueous  humor  and  is 
in  contact  with  the  iris.  On  its  posterior  side  it  rests  in 
a  concave  depression  of  the  vitreous  humor. 

The  convexity  of  the  lens  is  greater  on  the  posterior 
side.  In  old  age  the  lens  becomes  flatter  and  less  trans- 
parent. In  structure  the  lens  is  made  up  of  a  number 
of  concentric  layers,  or  lamina,  much  like  the  structure 
of  a  lily-bulb  or  onion. 

The  lens  is  held  in  place  by  a  ligament,  which  is 
attached  all  around  its  edge.  This  ligament  is  attached 
also  to  a  ring  of  muscle-fibres  at  the  front  edge  of  the 
choroid  coat.  This  muscle,  known  as  the  ciliary  muscle^ 
is  composed  of  both  circular  and  radial  fibres.     An  idea 


TUK   SPECIAL    SENSES  803 

of  the  relation   of  these  ])ails  may  he  ohtaiii<'<l  IVoni  the 
diaiirani  in  Fig.  130. 

The  lens  is  ehustic,  and  wlien  left  to  itself  its  sides  will 
bulire  out  and  beeonie  quite  convex,  but  tin*  susjiensory 


Fig.  130. — Section  showing  attachments  of  the  lens,  cm,  ciliarN- 
muscle  ;  cc,  front  edge  of  choroid  arranged  in  folds  called  the  ciliary 
processes;  S,  suspensory  ligament;  P,  pupil;  /,  iris;  0,  origin  of 
ciliary  muscle. 

ligament  is  constantly  under  tension,  thus  flattening  the 
sides  of  the  lens.  When,  however,  it  becomes  necessary 
for  the  lens  to  be  more  convex,  the  ciliary  muscle  con- 
tracts and  thus  relieves  the  tension  of  the  ligament. 

The  chief  function  of  the  lens  is  to  regulate  the 
amount  of  refraction  so  that  the  rays  of  light  will  meet 
and  form  an  image  on  the  yellow  spot  of  the  retina. 

How  we  can  see  distinctly  at  various  dis- 
tances.— iVs  long  as  the  distance  between  any  object 
and  a  fixed  lens  remains  the  same,  the  distance  of  the 
image  on  the  other  side  of  the  lens  will  remain  the  same. 
If  the  distance  of  the  object  is  changed,  the  i)osition  of 
the  image  will  be  shifted.  This  is  illustrated  in  Fig.  131. 
When  0  is  moved  towards  the  lens,  7*'  moNcs  farther 


304 


THIRD   BOOK   OF   PHYSIOLOGY 


away,  and  when  0  is  moved  away,  F  approaches  the  lens. 
Thus,  if  the  crystalline  lens  of  the  eye  were  fixed  in 
position  and  shape,  we  would  be  able  to  see  distinctly  only 
at  a  definite  distance.     If  the  distance  for  any  eye  hap- 


FiG.  lol. — Diagram  showing  how  the  focal  distance,  F^  depends  on 
the  distance  of  the  object.  0,  in  the  same  lens. 

pened  to  be  ten  feet,  say,  then  only  the  objects  at  that 
distance  could  be  seen  distinctly.     This  would  evidently 


Fig.  132. — Diagram  .showing  the  effect  of  lenses  of  different  curva- 
ture. 0  and  O  are  objects  at  the  same  distance  from  lens.  The  lens 
which  is  more  convex  brings  the  rays  together  at  a  shorter  distance 
from  the  lens. 

be  very  inconvenient,  and  so  nature  has  provided  a 
method  of  adjustment  which  is  very  simple  and  is  oper- 
ated without  any  attention  on  our  part. 


TIIK    SPEC^IAL    SENSES  305 

The  more  convex  any  lens  is,  the  nioie  it  will  refract  a 
ray  of  li<j;lit.  This  is  illnstrated  in  Fi<^.  132.  This  is 
the  ])rinciple  ntilized  in  the  eye,  and  the  convexity  of  the 
crystalline  lens  is  changed  in  the  manner  already  ex- 
plained, for  different  distances.  Thns,  if  the  upper  lens, 
Fig.  132,  is  just  the  right  convexity  to  throw  i^  apon  the 
retina,  then  the  convexity  of  the  lower  lens  is  too  great, 
and  F  there  falls  short  of  the  retina.  In  that  case  the 
cilijiry  nuiscles  relax  and*  the  tension  of  the  suspensory 
ligament  is  restored.  This  makes  the  lens  flatter,  and 
thus  the  image  is  moved  to  the  proper  distance. 

The  emmetropic  eye.— In  a  normal  eye  parallel 
rays  of  light  will  be  focused  on  the  retina  without  any 
action  of   the  ciliary  muscle.      For    near  objects    the 


Fig.  133. — Emmetropic  eye. 

rays  that  enter  the  eye  will  be  divergent,  and  then  the 
lens  will  become  more  convex  and  will  bring  the  rays 
together  at  the  same  point.  Such  an  eye  is  emmetropic, 
and  is  capable  of  adjustment  for  any  distance  to  within 
about  eight  inches  from  the  eye. 

The  myopic  eye. — When  parallel  rays  come  to  a 
focus  before  the  retina  is  reached,  the  eye  is  said  to  be 
myopic  (Fig.  134).      This  condition  may  result  from  too 

20 


306  THIED    BOOK    OF    PHYSIOLOGY 

great  a  curvature  of  the  cornea  or  the  lens,  or  it  may 
be  due  to  an  elongation  of  the  ball  of  the  eye.  By  refer- 
ence to  Fig.  131  it  is  plain  that  if  an  object  be  held 
near  the  eve,  a  certain  distance  mav  be  found  where  the 
image  will  fall  exactly  on  the  retina.  F(jr  distinct  vision 
an  object  must  always  be  held  close  to  such  g^n  eye.     The 


Fig.  134. —Myopic  eve. 

defect  is  called  short-sightedness.  It  can  be  corrected  by 
the  use  of  concave  glasses.  A  concave  lens  always  tends 
to  scatter  the  waves  of  light,  while  convex  lenses  always 
tend  to  bring  the  rays  to  a  focus.  Hence  concave  glasses 
may  be  ground  so  that  they  will  just  correct  the  defect 
in  the  convex  lenses  of  the  eye,  and  the  image  will  be 
thrown  upon  the  retina  as  in  the  normal  eye. 

The  hypermetropic  eye. — It  often  occurs  that 
even  when  the  lens  is  as  convex  as  the  eye  can  make  it, 
still  the  image  falls  beyond  the  retina  (Fig.  135,  c). 
This  may  result  from  the  fact  that  the  cornea  is  not  suf- 
ficiently convex,  or  the  distance  from  the  lens  to  the 
retina  may  be  less  than  in  the  normal  ej'e.  This  defect 
may  be  so  slight  that  only  very  near  objects  are  indis- 
tinctly seen,  or  it  may  be  so  great  that  even  the  parallel 
rays  from  objects  at  an  infinite  distance  may  be  focused 
beyond  the  retina.     Since  greater  refraction  of  the  rays 


THE    SPECIAL    SENSES  307 

is  needed,  it  is  plain  that  convex  glasses  will  correct  the 
defect. 

Such  an  eye  is  said  to  he  far-si ffhted.  Nearly  every  one 
who  has  passed  the  age  of  about  forty-five  years  is,  to 
some  degree,  far-sighted.     The  cause  is  that  the  cornea 


Fig.  135. — Hypermetropic  eye. 

becomes  less  convex  and  the  lens  less  capable  of  adjust- 
ment as  age  advances.  This  is  why  middle-aged  and  old 
people  wear  glasses  when  they  read  or  look  at  minute 
objects  near  by. 

Movements  of  the  eyes. — For  distinct  vision  it  is 
necessary  that  the  image  fall  upon  the  most  sensitive 
part  of  the  retina,  which  is  the  yellow  spot.  This  spot 
is  in  line  with  a  ray  of  light  that  would  pass  through  the 
centre  of  the  cornea,  the  pupil,  and  the  lens. 

One  can  see  indistinctly  all  four  walls  of  a  room  by 
taking  a  position  near  one  corner,  because  the  retina  lines 
the  interior  of  the  eyeball  almost  to  the  iris.  But  when 
we  wish  to  see  anything  distinctly,  we  must  look  straight 
at  it.  To  do  this  we  turn  the  head  or  move  the  eyes  in 
their  sockets. 

Six  muscles  are  attached  to  the  sclerotic  coat  of  each, 
eye.      Four   of    these   are   called  the   recti,   or  straight^ 


308 


THIED   BOOK   OF   PHYSIOLOGY 


muscles.     One  is  attached  above,  one  below,  and  one  on 
each  side. 

When  the  upper  one  contracts,  the  front  of  the  eye 
will  be  turned  upward,  and  each  of  the  other  three  will 
in  the  same  vray  turn  the  front  of  the  eye  to  the  side  to 
which   the   muscle   is   attached.      The   superior   oblique 


Fig.  136. — Muscles  of  the  eye.  1,  2,  3.  4.  recti  muscles  ;  4  is  oppo- 
site 2  and  cannot  be  seen  in  cut ;  5,  superior  oblique  muscle  ;  6,  pulley 
through  which  the  tendon  plays  ;  7,  inferior  oblique  muscle  ;  8,  optic 
nerve. 


muscle  is  peculiar  in  that  its  tendon  passes  through  a 
cartilaginous  ring  (Fig.  136,  6),  and,  passing  on,  is 
attached  to  the  side  of  the  eyeball.  The  ring  thus  acts 
as  a  fixed  pulley,  and  a  contraction  of  this  muscle  would 
tend  to  roll  the  ball  in  its  socket.  The  inferior  ohliqae 
muscle  also  tends  to  rotate  the  ball,  but  in  a  direction 
opposite   to   that    produced    by   the    super ioi'   oblique. 


THE    SPRCIAL    SENSES  309 

These  two  inuscles,  then,  are  antagonistic  to  each  other 
and  hold  the  ball  steadily  in  place. 

Effect  of  defective  eye-muscles. — It  is  evident 
that  if  any  one  of  the  muscles  attached  to  the  eyeball 
should  be  paralyzed,  or  should  be  too  short  or  too  long, 
the  ball  would  not  have  a  correct  position  in  its  socket. 
If  the  outside  recti  muscles  are  too  short  or  the  inside 
ones  should  be  paralyzed',  the  eyes  would  turn  outward. 
If,  as  often  hai^pens,  the  inside  rectus  pulls  harder  on 
the  ball  than  the  outside  one  does,  the  eye  will  be  turned 
inward,  and  cause  squinting  or  cross-eyes. 

Any  lack  of  balance  between  the  eye-muscles  will  result 
in  defective  vision,  and  will  also  be  objectionable  from  the 
stand-point  of  personal  appearance.  Fortunately,  a  skil- 
ful surgical  operation  will  usually  correct  such  defects. 

The  posterior  parts  of  the  eye. — Thus  fiir  we 
have  been  chietiy  concerned  with  the  descriptions  and 
functions  of  those  parts  of  the  eye  which  had  to  do  with 
the  formation  and  location  of  the  image.  These,  we  have 
seen,  are,  for  the  most  iDart,  in  the  anterior  regions  of  the 
eye.  It  remains  to  be  seen  how  the  image  is  received  by 
the  terminations  of  the  optic  nerve,  and  how  the  stim- 
ulus is  conducted  to  the  seat  of  perception  in  the  brain. 
This  is  elBfected  through  agencies  in  the  posterior  part  of 
the  eye. 

The  retina. — The  sclerotic  coat  is  on  the  outside  of 
the  eyeball.  It  is  composed  of  tough,  white  fibrous  ma- 
terial, and  is  usually  called  the  ''white  of  the  eye.'' 


310 


THIRD    BOOK    OF   PHYSIOLOGY 


^L 


The  next  coat  is  the  choroid, 
which  is  of  a  dark  color,  and  is 
very  vascular,  being  filled  with 
a  net- work  of  blood-vessels. 

The  innermost  coat  is  the 
retina,  which  will  now  l)e  more 
fully  described. 

The  retina  lines  the  whole 
posterior  cavity  of  the  eyeball 
and  extends  forward  nearly  to 
the  iris.  It  is  only  about  one- 
fiftieth  of  an  inch  thick  at  the 
point  directly  opposite  the  iris, 
where  it  is  thickest.  It  is 
composed  chiefly  of  terminals 
of  the  nerve-fibres  of  the  optic 
nerves,  with  certain  sustaining 
tissue  that  holds  the  nerve  ele- 
ments in  place. 

The  anatomist  distinguishes 
ten  ditlerent  layers  of  the  ret- 
ina, the  most  important  of 
which  are  pointed  out  in  Fig. 
137.     The  Avhole  distance  from 


Fig.  137.— Diagram  show-  F  F  to  L  L  in  the  figure  repre- 

ing  the  nerve  elements  of  ret-  ^^^^   ^^^   thickneSS  of  the  ret- 
ina ;   aa,  rods  ;  h,  cone  ;  c,  nu- 

cleus  of  cone;  cZ,  nucleus  of  i^^,    SO    that    the    parts    here 

rod ;  ji,  nerve-cell ;  oo,  fibres  shown  on  a  large  scale  cau  be 

of  optic  nerve;   LL,   internal  ^^^^    ^^^^,    ^^.    ^.^    ^^    ^    ^^^^^^ 
limiting  membrane  ;   PP,  pig- 
ment-cell laver.  microscope.     The  line  L  L  rep- 


THE   SPECIAL   SENSES 


311 


resents  the  limiting  membrane  which  lies  next  to  the 
vitreous  humor,  while  (Ijc  line  P  P  r(iprevSents  the  i)ig- 
ment-cell  layer  which  lies  adja- 
cent to  the  choroid  coat.  These 
are  respectively  the  tirst  and 
tenth  layers  of  the  retina.  The 
other  eight  layers  are  between, 
and  have  a  variety  of  structure, 
being  composed  mainly  of  nerve- 
cells,  nuclei,  nerve-fibres,  and 
special  nerve  terminals. 

The  ninth  layer  is  composed 
of  nerve- cells  of  special  forms 
called  7'ods  and  cones.  In  Fig. 
138  is  shown  one  of  each  of  these 
two  kinds  of  cells,  very  highly 
magnified.  Their  name — ''rod" 
and  ' '  cone"— is  plainly  suggested       ^^^^  i38.-llod  and  cone 

by    their    shape.       Three    or    four    from  the  retina.     R,  rod ; 

rods  are,  as  a  rule,  found  between   ^'  ^^^"'    ^'    P'^^'^'J   2, 

body ;  3,  nucleus. 
every     two     cones.        The     light 

passes  nearly  through  the  retina  before  it  reaches  these 

cells. 


The  yellow  spot  and   the   blind  spot.— Two 

spots  appear  on  the  posterior  wall  of  the  retina.  One 
is  a  white  circular  spot,  which  is  slightly  elevated,  form- 
ing the  optic  papilla.  This  is  the  point  of  entrance  of 
the  optic  nerve,  and  is  called  the  blind  spot^  because  it 
contains  no  nerve  terminals,  and  hence  an  image  falling 


312 


THIRD   BOOK   OF   PHYSIOLOGY 


upon  it  produces  no  sensation.  Near  by  is  another  spot 
which  is  circular  or  oval  in  shape  and  yellow  in  color. 
It  is  called  the  yellow  spot.     Its  diameter  is  only  about 

one-twenty-fourth     of     an 
inch.     Here   the  layer   of 
nerve- cells  is  thicker  than 
elsewhere,  and  in  the  ninth 
layer  only  cones  are  found. 
In  the  centre  of  the  yel- 
low spot   is  a   conical   de- 
X^ression.     where     all     the 
layers    of   the    retina    are 
removed      down      to      the 
cones,   and   the   dark   pig- 
ment layer  shows  through, 
making  the  depression  look 
like  a  hole  through  the  retina.     This  spot  is  called  the 
central  fovea.      It   is  a  condition  for  the   most  distinct 
vision  that  the  image  fall  upon  the  central  fovea. 

The  blind  spot  is  about  one-tenth  of  an  inch  from  the 
yellow  spot,  towards  the  inner  side  of  the  eye. 


4    68 

Fig.  139. — Retina  seen  on  its 
posterior  inner  surface.  1.  scle- 
rotica ;  2.  choroidea ;  3,  retina ; 
4,  the  optic  papilla ;  5,  central 
retinal  artery  ;  6,  a  slight  fold  of 
the  retina ;  7,  the  yellow  spot ; 
8,  its  central  fovea. 


The  size  of  the  image. — The  image  on  the  retina 
may  cover  a  large  portion  of  the  posterior  part  of  the 
retina,  but  only  a  very  small  portion  of  it  can  be  dis- 
tinctly seen.  The  whole  page  of  this  book  is  imaged  on 
the  retina  while  you  read,  but  not  more  than  a  single  let- 
ter can  be  seen  distinctly  at  one  time.  Reading  is  accom- 
plished by  moving  the  eyes  so  that  the  image  of  each 
letter  is  rapidly  swept  across  the  yellow  spot. 


THE    SI»K(MAL    SENSES  313 

The  smallest  object  which  can  be  seen  as  having  any 
dimension  must  form  an  image  at  least  large  enough  to 
reach  from  one  cone  to  the  next  adjacent  one  in  the 
central  fovea  of  the  yellow  spot. 

Experiment  shows  that  when  two  points  are  so  close 
together  that  lines  drawn  from  each  to  the  eye  make 
with  each  other  an  angle  of  fifty  seconds,  then  the  image 
of  these  two  points  on  the  retina  would  be  only  W^tt  inch 
apart.  The  distance  between  two  adjacent  cones  is  also 
6  00  0  of  an  inch.  Fifty  seconds  then  is  the  limiting  visual 
angle  for  seeing  two  points  as  separate.  Any  less  angle 
would  cause  the  two  points  to  appear  as  one.  This  is 
the  case  with  many  double  stars  which,  to  the  naked 
eye,  appear  as  one,  but  in  the  telescope  are  seen  to  be 
double. 

What  seeing  is. — Waves  of  light  from 'an  object 
are  refracted  so  as  to  form  an  image  on  the  rod  and  cone 
cells  of  the  retina.  These  waves  act  as  a  stimulus  and 
set  up  nervous  impulses  which  travel  along  the  fibres  of 
the  optic  nerve  to  the  base  of  the  brain,  and  thence  by 
other  neurons  to  the  seat  of  visual  sensation  in  the  occip- 
ital lobe  of  the  cerebrum.  The  seeing  is  in  the  brain  and 
not  in  the  eye.  If  the  optic  nerves  were  severed,  the  eye 
could  still  form  perfect  images  on  the  retina,  but  there 
would  be  no  vision. 

The  optic  nerves. — The  optic  nerves  arise  from  the 
base  of  the  brain  at  what  is  called  the  optic  chiasma. 
The  nerve-fibres  which  compose  the  optic  nerves  have 


3U  THIED    BOOK    OF   PHYSIOLOGY 

their  termination  in  tlie  seat  of  sensation  in  the  brain, 
but  on  their  way  from  the  eyes  they  meet  in  the  optic 
chiasma,  where  most  of  the  fibres  pass  across  to  the  other 
side,  as  shown  in  Fig.  140. 

Part  of  the  fibres,  however,  pass  on  to  the  brain  on  the 
same  side.     Thus  each  eye  sends  impulses  to  both  hemi- 


FiG.  140.— The  optic  nerves. 

spheres  of  the  brain  ;  and  even  if  one  side  of  the  brain 
should  be  paralyzed,  there  would  still  be  vision  from  both 
eyes. 

Advantage  of  two  eyes. — When  both  eyes  are 
used  an  image  is  formed  on  corresponding  parts  of  the 
retina  in  each  eye.  Similar  impulses  are  thus  sent  to 
each  hemisphere  of  the  cerebrum  and,  as  the  sensations 
agree,  an  object  is  seen  singly.  By  a  slight  pressure  of 
the  finger  against  the  side  of  one  eyeball,  the  inage  on 


Till-:    SPKCIAF.    SKXSES  315 

the  retina  may  l>e  shifted  so  that  its  position  does  not 
agree  witli  that  in  the  other  eye.  An  obje*et  tlien  api)eai-s 
distorted  or  double. 

By  the  use  of  two  eyes  all  objects  can  be  seen  witli 
greater  distinctness,  and  solid  objects  are  made  to  stand 
out  as  solids. 

Color  sensations. — The  eye  is  so  constructed  that 
different  nervous  impulses  are  produced  by  the  different 
wave-lengths  of  light.  This  gives  us  the  ability  to  dis- 
tinguish coloi-s,  for  difference  in  color  results  only  from 
difference  in  the  wave-length  of  light. 

These  waves  have  been  measured,  and  it  is  found  that 
when  395.000,000.000.000  of  them  flow  into  the  eye  in  one 
second,  the  sensation  will  be  what  we  call  red.  When 
the  number  is  7G0. 000. 000. 000. 000  per  second,  the  sen- 
sation is  called  violet.  The  waves  are  longest  for  red 
and  shortest  for  violet,  while  various  other  wave-lengths 
produce  all  the  intervening  colore. 

Some  able  scientists  believe  that  the  nerve-terminals  in 
the  eye  are  of  three  distinct  kinds.  One  kind,  when 
stimulated  alone,  will  give  rise  to  the  seiLsation  of  red  ; 
another  kind,  green  :  and  a  third  kind,  violet.  AVhen 
all  three  are  stimulated  equally,  the  combined  sensation 
is  white.  Grav  is  a  low  dearree  of  whiteness.  All  other 
coloi-s  are  mixtures  of  certain  proportions  of  these  three 
primary  color  sensations. 

The  eyes  of  some  persons  are  deficient  in  ability  to  dis- 
tinguish certain  colors.  Such  pei-sons  are  said  to  be 
color-bliiid. 


316  THIED   BOOK   OF   PHYSIOLOGY 

The  iuability  to  distinguish  red  and  green  is  the  com- 
mon defect. 

About  four  men  out  of  every  hundred  and  one  woman 
out  of  every  two  hundred  are  said  to  be  color-blind. 

Nature's  provision  for  the  protection  of  the 

eyes. — Since  the  eye  is  such  a  delicate  and  useful  organ, 
it  must  be  well  protected  from  possible  harm,  for  an 
injury  to  it  is,  indirectly,  an  injury  to  the  whole  organ- 
ized body. 

The  safeguards  placed  about  the  eye  are  (1)  its  position 
in  a  bony  socket,  (2)  the  eyelids  and  eyebrows,  (3)  the 
tears  and  oil  secretions,  and  (4)  the  sensitive  conjunc- 
tiva. 

Any  flat  object,  as  a  book  or  the  open  hand,  pressed 
over  the  region  of  the  eye,  will  be  arrested  before  it 
touches  the  eyeball.  Thus  the  eye  is  protected  bj'  its 
deep  position  in  a  bony  socket. 

Tlie  eyebrows  keep  sweat  or  other  liquid  from  run- 
ning down  into  the  eyes. 

The  eyelids  and  lashes  are  a  constant  protection  against 
dust  and  insects,  and  by  frequently  closing  and  opening, 
the  lids  wash  the  surface  of  the  eye  and  keep  it  uniformly 
moist. 

The  tears  are  very  necessary  for  keeping  the  exposed 
part  of  the  eye  clear  and  transparent.  Beneath  the  skin 
near  the  outer  end  of  the  eyebrows  is  a  racemose  gland 
which  secretes  a  liquid  called  tears,  and  pours  it  through 
a  dozen  or  more  ducts  onto  the  surface  of  the  eye.  The 
ducts   open   beneath  the   upper   eyelid,   near   the  outer 


TlIK   SPECIAL   SENSES 


317 


corner  of  the  eye.  At  the  inner  corner  of  the  eye  is  a 
provision  for  cunvinj^  any  excess  of  teiirs  into  the  nos- 
trils. This  can  Ix'  understood  from  an  examination  of 
Fi^'.  141. 

At  the  inner  anjj^le  of  the  eye,  on  each  eyelid,  may  be 
seen  a  slij^^ht  elevation.  These  are  the  lachrymal  impilloe. 
On   the  summit  of  these  is  a  small  oi)euing  called  the 


.K.>..-v--.::----.v:ii5^ 


Fig.  141. — The  left  eye,  with  a  portion  of  the  eyelids  removed,  to 
exhibit  the  lachrymal  canals  and  sac.  1,  lachrymal  canals;  2,  com- 
mencement of  these  on  the  lachrymal  papilla; ;  4,  edges  of  the  eye- 
lids ;  5,  lachrymal  sac  ;  6,  internal  palpebral  ligament. 


lachrymal  punetum.  Tears  enter  these  openings,  and  are 
carried  back  through  the  canal  to  the  lachrymal  sac,  and 
escape  thence  into  the  nose. 

In  the  eyelids  are  also  a  number  of  small  glands  which 
secrete  an  oily  substance  and  pour  it  out  on  the  edges  of 
the  lids. 

The  tears  keep  the  cornea  always  clean  and  moist,  and 


318  THIED   BOOK   OF   PHYSIOLOGY 

the  oil  keeps  the  tears  from  flowing  over  at  the  edge  of 
the  lids. 

The  inuer  surface  of  both  lids  and  the  whole  visible 
front  of  the  eyeball  are  covered  by  a  delicate  and  very 
sensitive  mucous  membrane  called  the  conjunctiva.  The 
sensitiveness  of  this  lining  quickly  calls  attention  to  the 
presence  of  any  foreign  substance  in  the  eye. 

Care  of  the  eyes. — Although  every  one  places  a 
high  estimate  upon  the  value  of  his  eyes,  yet  no  other 
organ  is  more  frequently  misused.  The  eye  has  wonder- 
ful powers  of  recovery  from  the  effects  of  mistreatment, 
but  sooner  or  later  some  weakness  of  the  eyes  will  appear 
if  they  are  persistently  abused. 

The  reading  of  fine  print  is  injurious.  Reading  by 
sunlight  or  a  very  strong  artificial  light  will  injure  the 
retina.  Eeading  by  twilight  or  a  weak  and  flickering 
artificial  light  will  strain  the  eyes.  It  is  injurious  to 
read  on  a  railroad  train,  because  the  jolting  requires  a 
constant  readjustment  of  the  lens. 

The  habit  of  reading  while  lying  on  a  lounge  or  after 
going  to  bed,  works  a  serious  injury  to  the  eyes,  and  has 
been  the  direct  cause  of  blindness.  Holding  a  book  too 
close  to  the  eyes  will  strain  the  adjusting  mechanism  and 
cause  short-sightedness.  One  should  not  bend  over  and 
look  down  upon  the  work  in  which  he  is  engaged.  A 
book  should  be  held  in  front  about  fourteen  inches  away 
for  a  normal  eye. 

The  light  should  be  admitted  at  the  rear  and  left  side 
of   the  room  where  j^upils  study  and  write  or  do  any 


TIIK    SPECIAL    SENSES  319 

work  requiring  a  constant  use  of  the  eyes.  Artificial 
light  should  always  fall  over  the  left  shoulder  upon  the 
page  of  a  book. 

If  the  eyes  smart,  pain,  or  have  a  full  feeling,  they 
need  rest,  and  should  l>e  examined  by  an  oculist  for  any 
defect  which  might  be  corrected  by  glasses.  Permit  only 
a  perfectly  reliable  and  competent  physician  or  oculist 
to  prescribe  for  the  eyes. 

Maintain  a  healthy  tone  of  the  whole  system  and  the 
eye.s  will  be  stronger  to  meet  the  demands  which  are  con- 
stantly made  upon  them. 

Alcohol  seriously  affects  the  eyes  by  its  injurious 
effects  upon  the  whole  body,  thus  decreasing  or  poison- 
ing the  source  of  nourishment  to  the  eyes,  and  also  di- 
rectly by  its  paralyzing  effect  upon  the  optic  nerve  and 
by  the  intiammation  which  results  from  the  congested 
blood-vessels.  Blood-shot  eyes  are  marks  of  the  alcohol 
drinker. 

The  use  of  tobacco  also,  particularly  the  smoking  of 
cigarettes,  frequently  works  serious  injury  to  the  organs 
of  vision.  This  is  particularly'  true  of  those  who  are 
pupils  in  school  and  those  whose  work  is  indoors.  Doc- 
tors often  refuse  to  treat  the  eyes  unless  the  patient  will 
cease  from  smoking,  at  least  during  the  time  of  treat- 
ment. 

THE   EAR 

The  second  great  medium  in  which  we  always  must 
live  is  the  air.  It  is  natural  that  we  should  have  an 
organ  which  is  capable  of  receiving  any  disturbance  in  the 
air  and  applying  it  as  a  stimulus  to  the  ends  of  a  nerve 


820  THIED   BOOK   OF   PHYSIOLOGY 

so  as  to  produce  a  sensation  in  the  brain.    Such  an  organ 
is  the  ear,  and  the  sensation  produced  is  called  sound. 

The  nature  of  air- waves. — Light- waves  have  been 
explained  as  a  series  of  undulations  which  might  be 
compared  to  the  undulating  waves  which  are  seen  on 
water.  But  waves  of  air  that  produce  sound  are  very- 
different  from  light-waves. 

If  air  could  be  seen  while  it  is  carrying  sound-waves  it 
would  be  noticed  that  at  one  point  the  particles  would 

^^e   crowded  together :    a 

^..5^i^?2^xii^^-     ;  -^-^^^^^^v       little     farther     on     they 


ji-??.'-^' 


'^'^ "'    \:.  ^^r.-^^  would     be    more    widely 


■yr-M'': 


■''*?^ 


■i^^^^^^^^^:.>^^%        separated,    and    still    far- 
""^l^i^^^^^^^^^^^^vl^-  ther      they      would       be 

"^'^-..i^.''%'  crowded    again,    and     so 

*%:^%  on.      The    crowded    con- 

dition of  the  air  is  called 

Fig.   142. — Condensations  and  rare-  . 

f    ..       .      .  a   condensation,    and    be- 

factions  m  air-waves. 

tween  the  condensations 
are  the  rarefactions.  This  condition  is  represented  in 
Fig.  142,  where  a  vibrating  body  at  O  is  sending  out 
condensations  and  rarefactions  in  all  directions.  Only  a 
small  section  of  the  waves  is  shown  in  the  figure. 

When  the  air  is  very  much  condensed  and  rarefied  the 
sound  is  intense  or  loud.  This  is  the  condition  of  the 
air  close  to  a  vibrating  body,  but  the  amount  of  conden- 
sation grows  less  and  less  as  the  distance  increases,  and 
thus  sounds  are  faint  when  the  vibrating  body  is  far  away. 

Each  wave  of  sound  is  composed  of  one  condensation 


THE   SPECIAL   SENSES  321 

and  one  rarefaction.  When  the  waves  are  very  close  to- 
gether, so  that  a  great  niinilx^r  of  them  reach  the  ear  in 
one  second,  a  note  having  a  high  pitch  is  prodnced. 
These  waves  travel  through  the  air  at  the  rate  of  about 
1100  feet  in  one  second.  They  move  fiuster  when  the  air 
is  warm  and  slower  when  it  is  cold.  When  the  number 
of  waves  per  second  is  about  sixteen,  they  begin  to  pro- 
duce a  sensiition  of  a  very  low  sound.  As  the  numl^er 
of  waves  increases,  the  pitch  rises,  until,  when  the  num- 
ber becomes  about  40,000  in  a  second,  the  ear  is  no 
lonf]rer  affected  bv  them. 

The  ear. — It  is  difficult  to  decide  between  thi?  eye 
and  the  ear  as  to  which  is  of  greater  service  to  man.  It 
appeal's  that  those  who  are  blind  are  capable  of  a  better 
sort  of  mental  culture  through  their  eai'S  than  those  who 
are  deaf  and  are  compelleil  to  gain  their  knowledge 
chiefly  through  their  eyes. 

The  ear  is  a  very  delicate  and  complex  organ,  and 
some  of  its  parts  are  exceedingly  difficult  to  explain. 
The  subject  may  be  discussed  under  three  heads, — the  ex- 
ternal ear  J  the  middle  ear.  and  the  internal  ear.  The  first 
two  are  concerned  only  in  receiving  and  ti^nsforming 
the  sound-waves  so  that  they  may  properly  excite  the 
terminals  of  the  auditory  nerve.  These,  then,  are  simi- 
lar in  function  to  the  parts  in  the  front  of  the  eye  which 
formed  and  located  the  image  on  the  terminals  of  the 
optic  nerve. 

The  external  ear. — The  e.vternal  ear  is  composed  of 
the  pinna  and  meatus.     The  pinna  is  the  part  of  the  ear 

21 


322 


THIED   BOOK   OF   PHYSIOLOGY 


that  projects  from  the  side  of  the  head.     It  is  composed 
of  elastic  cartilage  covered  with  skiu.     As  may  be  seen 

in  Fig.  143,  the  outer  rim  is 
called  the  helix.  The  soft, 
pendent  i)art  at  the  lower 
end  is  tlie  lobe.  The  deep 
depression  near  the  centre  is 
the  concha,  which  is  partly 
divided  by  the  commence- 
ment of  the  helix.  At  tlie 
bottom  of  the  concha  i^  the 
entrance  to  the  meatus.  The 
pinna  collects  the  waves  from 
a  larger  area  of  air  and  di- 
rects them  to  the  month  of 
the  meatus.  Thus  the  sound 
is  made  more  intense,  just  as 
a  high  tide  may  be  caused  at 
the  narrow  head  of  a  bay  by 
the  feeble  waves  collected  from  a  large  area  at  the  mouth 
of  the  bay. 

In  many  animals  the  pinna  can  be  freely  moved  by  the 
action  of  muscles  which  are  attached  to  it.  3Iuscles  are 
also  provided  for  this  purpose  in  man,  but  so  seklom 
have  they  l)een  used  that  in  most  people  they  have  lost 
their  power. 

The  second  part  of  the  external  ear  is  the  auditory 
meatus,  or  caiial.  which  is  about  one  inch  long,  and  ex- 
tends from  the  concha  to  the  drum-head  of  the  middle 
ear.     The  first  part  of  the  canal,  about  one-half  incli  in 


Fig.  143.— Pinna  of  ear. 
H,  helix ;  C,  concha ;  L, 
lobe  ;  E,  entrance  to  audi  to ry 
meatus. 


THE   SPECIAL   SENSES 


323 


leiifrtli,  is  formed  of  cartilage,  and  tlie  remain  in*;  part  is 
througli  bone.  The  wliole  is  lined  with  a  very  thin  skin, 
which  also  covei*s  the  outer  side  of  the  drum-heiwl.  Be- 
neath the  skin  in  the  cartila<;inou.s  portion  are  numer- 
ous j^lands  which  secrete  the  ear  wax.  This  wax  is  bitter 
and  sticky,  and.  with  the  aid  of  hairs  at  the  entrance  of 
the  canal,  keeps  insects  and  dust  from  reaching  the 
drum  head. 

The  middle  ear.— The  middle  ear  is  a  cavity  in  the 
temporal  bone  between  the  external  and  internal  ears. 
It  is  called  the  ti/mpanum,  or  ear-drum,  because  it  contains 


Fig.  144. — The  tympanic  membrdne  and  the  ossicles  of  the  middle 
ear.  /n,  meatus  ;  f.  tympanum  :  h.  malleus,  or  hammer ;  o,  incus,  or 
anvil ;  s,  stapes,  or  stirrup. 


air.  and  a  membrane  is  stretched  between  it  and  the 
meatus.  Upon  this  membrane  the  air-waves  beat  as 
upon  the  head  of  a  drum.    The  drum  communicates  with 


324  THIRD.   BOOK    OF   PHYSIOLOGY 

the  outside  air  through  the  Eustachian  tube,  which  con- 
nects it  with  the  pharynx. 

Within  the  drum  is  a  chaiu  of  bones  which  are  articu- 
lated to  each  other,  one  end  of  the  chain  being  fastened 
to  the  drum-head  and  the  other  to  the  oval  window  of 
the  inner  ear.  The  bones  are  called  the  ossicles  of  the 
middle  ear.  Their  relation  to  each  other  and  to  the 
tympanum  may  be  seen  in  Fig.  144. 

The  shape  of  the  bones  has  suggested  the  names  ham- 
me7',  anvil,  and  stirnq).  The  corresponding  Latin  names 
commonly  used  are  malleus,  incus,  and  stapes. 

The  purpose  of  the  middle  ear  is  to  receive  the  feeble 
waves  which  beat  upon  the  drum- head  and  convert  them 
into  vibrations  of  greater  force,  so  that  they  may  prop- 
erly affect  the  liquid  which  fills  the  spaces  of  the  inner 
ear.  This  is  done  by  the  tympanic  membrane,  or  drum- 
head, and  the  chain  of  bones. 

The  tympanic  membrane,  or  drum-head.— 

The  chief  agency  for  intensif^'ing  the  vibrations  is  the 
drum-head.  In  shape  and  structure  it  is  admirably 
adapted  to  this  end.  It  is  composed  of  three  layers,  the 
outer  one  being  a  continuation  of  the  skin  w^hich  lines 
the  meatus,  and  the  inner  one  being  the  mucous  mem- 
brane which  lines  the  whole  interior  of  the  drum.  The 
middle  layer  is  the  essential  one.  It  is  composed  of 
radial  and  circular  fibres  of  connective  tissue  which  are 
alwaj^s  stretched  and  kept  tense  by  a  muscle  which  pulls 
on  the  handle  of  the  hammer.  Thus  the  membrane  is 
made  to  take  the  shape  of  a  funnel  with  its  apex  at  the 


TIIK    SPFClAf.    SF.XSES 


325 


point  of  attachment  to  the  hammer.  Tlie  sides  of  this 
funnel  are  stretched,  but  do  not  piuss  straij^ht  from  the 
rim  to  the  apex.  They  apparently  sag  towards  the  centre 
of  the  funnel,  thus  l)eing  convex  towards  the  meatus. 
This  is  important,  for  it  is  chietly  by  this  arrangement 
that  the  force  of  a  sound-wave  is  intensified.  Tlie  me- 
chanical principle  involved  may  be  easily  understood 
by  reference  to  the  dia- 
gram, Fig.  145,  which  rep- 
resents the  outlines  of  the 
drum-head.  The  radial 
fibres  are  stretched  from 
the  apex  to  the  base  of 
the  cone,   and  the  circular 


Fig.    14o. — Diagram    showing 
mechanical  action  of  tympanum. 


fibres  keep  the  sides  convex  towards  the  centre.  Xow, 
any  pressure  against  the  inner  sides  of  a  and  h  in 
the  direction  of  the  arrows  would  relieve  their  tension 
and  permit  the  apex  to  move  towards  c,  in  which  direc- 
tion it  is  constantly  pulled  by  the  handle  of  the  ham- 
mer. When  the  pressure  ceases,  the  apex  will  at  once 
be  brought  back  to  its  former  position  by  the  tension  of  a 
and  b.  The  sides  may  move  back  and  forth  through  a 
considerable  distance,  while  the  apex  will,  as  a  result,  be 
moved  back  and  forth  only  a  very  short  distance,  but  with 
proportionately  greater  force.  Thus  sound-waves  may 
exert  a  considerable  force  on  the  handle  of  the  hammer. 


The  ossicles  of  the  ear-drum.. — The  function 
of  the  three  bones  in  the  drum  is  to  transfer  the  vibra- 
tions from  the  drum  head  to  the  inner  ear,  and  to  still 


326  THIRD    BOOK    OF    PTTYSTOLOGY 

further  intensify  the  vibration  at  a  sacrifice  of  distance 
moved. 

The  bones  are  held  in  place  by  ligaments,  and  are 
closely  jointed  to  each  other.  They  act  together  as  a 
lever,  having  its  fulcrum  at  F  (Fig.  146).  Thus  the 
power  arm  of  the  lever  is  the  distance  from  the  vertex 
of  the  drum-head  to  7^,  while  the  resistance  arm  is  only 
from  F  to  the  end  of  the  long  process  of  the  anvil.  The 
power  arm  of  this  lever  is  found  to  be  one  and  one-half 
times  as  long  as  the  resistance  arm,  and  so  the  force  is 
increased  one  and  one-half  times  and  the  distance  moved 
is  made  proportionately  less.  The  back  and  forth  move- 
ment of  the  stirrup  does  not  exceed  about  2 io  of  an  inch. 

The  Eustachian  tube. — The  pressure  of  the  air 
within  the  drum  should  be  the  same  as  that  of  the  air 
outside.  Air-pressure  is  constantly  changing  at  any 
point  on  the  earth,  as  is  shown  by  the  changes  in  the 
barometer,  and  also  the  pressure  is  different  at  different 
altitudes. 

In  order  that  man  might  retain  his  power  of  hearing 
while  he  is  subject  to  these  frequent  changes,  it  is  neces- 
sary that  a  tube  connect  the  outside  air  with  the  drum. 
This  is  the  purpose  of  the  Eustachkin  tube,  which  is  shaped 
like  a  trumi^et,  and  is  connected  by  its  small  end  to  the 
drum  and  by  its  large  end  to  the  pharynx.  It  is  made 
of  thin  cartilage,  so  that  it  usually  stands  open. 

Air  may  be  forced  from  the  mouth  into  the  drum,  or 
may  by  suction  be  drawn  from  it.  In  either  case  a  dif- 
ference of  air  tension  is  caused  within  and  without  the 


THE   SPECIAL   SENSES  327 

drum.  :ni(l  lieariiif:;  becomes  indistinct  and  confused. 
Tliis  will  colli  iiuic,  tlioui^li  nose  :ni(l  mouth  ])c  now  open, 
loi-  the  hir<;e  opening  of  the  tube  is  loosely  closed  by 
certain  muscles  in  the  ])hai yiix  which  are  concerned  in 
the  act  of  swallowing.  When  we  swallow,  then,  the 
l)assage  through  the  tube  is  free,  and  the  equjil  tension 
of  the  air  is  restored. 

When  the  i)harynx  is  inilamed,  as  from  colds,  the 
Eustachian  tube  often  becomes  partly  or  wholly  closed, 
thus  causing  a  roaring  and  feeling  of  fulness  in  the 
drum.  I' 

Oipenings  into  the  drum. — The  Eustachian  tube  is 
the  only  opening  through  which  substances,  such  as  gases 
and  liquids,  can  pass  into  and  from  the  middle  ear,  or 
drum.  There  are  three  other  openings,  however,  through 
which  waves  or  other  disturbances  may  easily  pass  in  or 
out.  These  are  all  covered  with  thin  membranes.  One 
is  the  tympanic  membrane,  which  has  already  been  de- 
scribed, and  the  other  two  are  the  oval  and  circular  win- 
dows which  open  into  the  internal  ear.  There  are,  also, 
openings,  near  the  top  of  the  drum,  into  air-chambers 
in  the  temporal  bone.  These  chambers  are  called  the 
tiiaslokl  cells. 

Size  of  parts  of  the  drum.— The  student  is  apt 
to  get  the  idea  that  the  parts  just  described  are  much 
larger  than  they  are  in  fact.  A  statement  of  the  size  of  a 
few  parts  may  assist  in  getting  a  correct  idea  of  the  size 
of  all. 


328 


THIED    BOOK   OF   PHYSIOLOGY 


The  tympanic  membrane  is  not  quite  one-half  inch  in 
diameter.  The  length  of  the  malleus,  or  hammer,  is 
nearly  seven-tenths  of  an  inch.     The  total  lensrth  of  the 


Fig.  146. — Diagram  showing  the  relative  position  of  the  three  parts 
of  the  ear.  //i,  meatus  ;  ^?n,  tympanic  memhrane  ;  i.  tympanum  ;  A, 
malleus  ;  a.  incus  ;  .s,  stapes  ;  o.  oval  window  ;  en^  Eustachian  tube ; 
sc,  semicircular  canals  ;  r,  vestibule  ;  ^,  cochlea  ;  F.  fulcrum  of  the 
lever  formed  by  the  ossicles. 

stapes,  or  stirrup,  is  not  quite   two-tenths  of  an  inch. 
The  weight  of  all  the  bones  together  is  only  a  few  grains. 


The  internal  ear.— The  relation  of  the  three  parts 
of  the  ear  may  be  learned  by  an  observation  of  the  dia- 
gram in  Fig.  146.  The  sound-waves  pass  in  through  the 
meatus,  in,  and  cause  a  vibration  of  the  tympanic  mem- 


TriK    SPECIAL    SENSES  329 

brane,  tni.  The  chain  of  hones  acts  as  a  lever  witli  the 
fulcruiu  at  J']  and  transmits  the  vibrations  to  tlic  oval 
window,  (>,  the  entrance  into  the  third  division  of  the 
ear. 

The  internal  ear  is  called  the  lahyrinth  because  of  its 
many  winding  passage-ways.  Tlie  labyrmth  is  an  irregu- 
lar chamber  in  the  hard  part  of  the  temporal  bone.  It 
may  be  described  as  composed  of  three  parts, — the  vesti- 


FiG.  147. — The  right  labyrinth,  viewed  outwardly  in  front,  magni- 
fied two  and  a  half  times.  1,  vestibule  ;  2,  oval  window  ;  3,  round 
window ;  4,  superior  semicircular  canal ;  5,  posterior  semicircular 
canal;   G,  inferior  semicircular  canal  ;   7,  ampullae;   8,  cochlea. 

hule^  the  semicircular  canals,  and  the  cochlea.  These  are 
simply  cavities  in  the  hard  bone.  If  some  plaster  of 
Paris  were  poured  into  these  cavities  and  allowed  to 
remain  there  till  it  would  harden  and  form  a  cast,  it 
would,  when  cut  out,  have  the  form  shown  in  Fig.  147. 
These  cavities  are  called  the  osseous  labyrinth,  as  distin- 
guished from  another  which  is  contained  within  it  and 
known  as  the  membranous  lahyrinth. 

The   osseous   labyrinth. — The    osseous,    or    bony, 
vestibule  lies  between  the  cochlea  and  the  semicircular 


830  TIUVJ)    BOOK    OF   PHYSTOLOOY 

canals.  On  its  front  side,  that  is  the  side  towards  the 
tympanum,  is  the  oval  loindow,  which  is  covered  with  a 
membrane  to  which  the  stirrup  is  attached.  Below  is 
the  round  icindoic.  covered  with  a  thin  membrane  which 
separates  the  liquid  within  the  vestibule  from  the  air  in 
the  middle  ear. 

In  the  back  part  of  the  vestibule  are  five  holes,  wdiich 
are  the  openings  into  the  semicircular  canals.  These 
canals  are  not  complete  circles,  but  arch  over  somewhat 
in  the  shape  of  a  horseshoe,  both  ends  opening  into  the 
vestibule.  Two  of  the  ends  unite  and  pass  together  into 
the  vestibule,  and  hence  there  are  but  five  openings  as 
seen  from  within  the  vestibule. 

The  plane  of  each  of  the  semicircular  canals  is  at  right 
angles  to  the  planes  of  the  other  two.  just  a,s  the  three 
faces  of  a  cube  that  meet  at  one  corner  are  each  at  right 
angles  to  the  other  two.  This  is  important,  as  will  be 
explained  later  on. 

The  osseous  cochlea  is  a  spiral  canal  resembling  in 
shape  the  interior  of  a  snail  shell,  and  hence  its  name. 

The  axis  of  the  cochlea  is  a  conical  pillar  of  bone  called 
the  modiolus.  The  canal  passes  sj^irally  around  the  modi- 
olus, making  two  and  one-half  turns. 

A  thin  spiral  shelf  of  bone,  called  the  spiral  lamina, 
projects  from  the  modiolus  much  as  the  blades  of  steel 
project  from  the  central  axis  of  an  augur.  The  spiral 
lamina  extends  about  half-way  across  the  canals,  as  shown 
in  Fig.  148.  The  remaining  distance  across  the  canal  is 
filled  in  by  tlie  membranous  cochlea,  which  will  later  be 
described.     Thus,  the  osseous  canal  is  divided  into  two 


TIIK    SIM^^>(UAL    SF.NSKS 


381 


nearly  equal  channels  thronghont  its  w  liolo.  l(»ngtli.  The 
MpjK'r  one  connnunieatcs  at  its  hiusc  witli  the  vestibule, 
and  so  is  callcMl  tln^  Ncstibnlsu" 
passjig(\ 

The  base  of  the  lower  one  is 
over  the  round  window,  through 
the  membrane  of  which  it  may 
communicate  with  the  tympanum, 
and  so  it  is  called  the*  lympanic 
passage.  The  two  are  connected 
only  b}^  a  small  orifice  at  the  top 
of  the  canal. 

The  whole  labyrinth  is  lined 
with  x^eriosteum,  which  secretes 
a  fluid  called  perilymph,  with 
which  the  labyrinth  is  filled. 


Fig.  148.— The  cochlea 
luid  open,  its  summit 
turned  upward,  mtigni- 
liod  three  diameters.  1, 
2,  3,  the  tympanic  pas- 
sage ;  4,  5,  G,  tlie  vestibu- 
lar passage ;  7,  8,  osseous 
spiral  lamina;  9,  mem- 
branous spiral  lamina ; 
10,  orifice  of  communica- 
tion of  the  two  passages 
at  the  summit  of  the 
cochlea;  11,  12,  termina- 
tion of  the  osseous  and 
membranous  spiral  lami- 
n:e. 


The  membranous  laby- 
rinth. -The  membranous  lahy- 
rlnth,  shown  in  Fig.  149,  is  nearly 
the  form  and  shape  of  the  bony 
labyrinth  in  which  it  is  enclosed. 
It  occupies  about  two-thirds  of 
the  space  in  the  bony  cavity  and 
partly  floats  in  the  i^erilymph.  It  is  comi^osed  of  three 
parts,  having  names  of  the  corresponding  parts  of  the 
bony  labyrinth,  and  is  filled  with  a  liquid  called  endo- 
lymph. 

In  the   membranous  vestibule   are   two   pouches,    the 
smaller   called   the  saccukj  and   the  larger,   the  utricle. 


332 


THIRD    BOOK    OF   PHYSIOLOGY 


These   are   fastened   together,    but  do  not  communicate 
except  through  the  Y"-shaped  tube  called  the  vestibular 

aqueduct,   sliown  in  Fig. 

Connected  to  the  utri- 
cle are  the  three  mem- 
branous semicircular 
canals  which  are  lightly 
attached  along  one  side 
to  the  bony  canal. 

A  division  of  the  au- 
ditory nerve  enters  the 
saccule,      utricle,      and 


^C^     — ^6 

Fig.  149. — The  membranous  laby- 
rinth, magnified  two  and  a  half  times. 
1,  utricle ;  2,  saccule ;  3,  semicircu- 
lar canals ;  4.  ampullae  of  semicircu- 
lar canals  ;  o,  vestibular  aqueduct ; 
6,  membranous  cochlea ;  7.  canal 
connecting  saccule  and  membranous 
cochlea. 


semicircular  canals,  and 
at  these  points  the  membrane  closely  adheres  to  the 
bone.  At  the  entrance  to  the  semicircular  canals  and 
on  spots  in  the  membranous  labyrinth  are  epithelial 
cells  of  a  peculiar  formation,  known  as  hair-cells.  These 
are  directly  surrounded  by  a  liquid  somewhat  thicker 
than  the  endolymph,  and  in  it  are  embedded  numerous 
small  crvstals  of  calcium  carbonate,  known  as  the  otoliths. 
In  these  hair-cells  the  nerve-fibres  of  the  vestibular 
branch  of  the  auditory  nerve  end.  These,  however, 
probably  have  no  part  in  producing  the  sensations  of 
sound. 

The  membranous  cochlea  is  a  three-sided  tube  with 
one  side  attached  to  the  bony  wall  of  the  canal  and  the 
opposite  corner  to  the  edge  of  the  spiral  lamina.  Thus, 
it  completes  the  division  of  the  bony  canal  into  two 
parts.     In   fact,    the  canal  of  the   cochlea  ma}'  be  con- 


TllK    SPECIAL    SENSES 


333 


sidered  as  divi(l<Kl  into  tliroe  spiral  tiil>es, — the  vestibular 

tnlH'.   tlif    fi/iHjKUii'c    tuhc.   and  the  monhnfuniis  tnbf    Ik?- 

twcon    ihv  othiT  two  and   on   the 

outer  side  of  the  eanal.     In  Fig. 

151    is   shown    a   eross-section   of 

one   of    the    bony   eanals   of   the 

cochlea. 

The  membranous  canal,  ur  pas- 
sage, is  filled  with  endoly-mph  and 
winds  about  with  the  other  pas- 
sages to  the  top  of  the  cochlea, 
where  it  is  closed.  Its  only  open 
ing  is  at  its  base  through  a  small 
canal  into  the  saccule.  See  Fig. 
140.  7. 


Fig.  150.— Diagram  of 
acoustic  epithelium.  1, 
acoustic  hair-cell ;  2,  sup- 
porting cell ;  3,  immature 
cell. 


The  organ  of  Corti.— The 
membranous  canal  of  the  cochlea 
is  the  most  essential  part  of  the 
organ  of  hearing.  On  its  floor 
is  the  organ  of  Corti.  where  the 

nerve-fibres   receive   the   impulses   that   arise   from   the 
vibrations  of  sound-waves. 

By  reference  to  Fig.  152  it  is  seen  that  a  membrane  is 
stretched  from  the  edge  of  the  spiral  lamina  at  O  to  the 
wall  of  the  cochlea  at  W.  This  is  the  basilar  membrane. 
Upon  it  stand  the  rods  of  Corti  and  the  hair-cells. 

The  rods  are  comparatively  stiff  and  are  arranged  in 
an  inner  and  an  outer  row.  The  tops  of  the  two  rows 
are  bent  towards  each  other  and  connected,  thus  forming 


334 


TIIIED    BOOK   OF   PHYSIOLOGY 


the  tunnel,  A.  The  base  of  the  rods  are  attached  by 
broad  feet  to  the  basilar  membrane.  About  4500  i)airs 
of  these  rods  are  placed  along  the  course  of  the  canal. 

On  the  inner  side  of  the  tunnel  formed  by  the  rods  is 
a  row  of  hair-cells,  and  on  the  outer  side  there  are  three 
or  four  rows  of  the  same  kind  of  cells.     (Fig.  152.) 


•-   ;-';!i=-ii~fir   A 


Fig.  151. — Cross-section  of  one  of  the  canals  of  the  cochlea,  show- 
ing the  three  passages.  1,  bon}-  wall  of  cochlea  ;  2,  position  of  modio- 
lus ;  3,  bone  of  spiral  lamina ;  4,  periosteum  ;  5,  basilar  membrane ; 
G,  under  the  arch  of  Cord's  fibres  ;   7,  cochlear  nerve  ;  8,  ganglion. 


A  fibre  of  the  auditory  nerve  is  attached  to  each  of 
the  hair-cells.  There  are,  in  the  cochlea,  about  16,000 
of  these  cells. 

The  basilar  membrane  is  stretched  from  side  to  side, 


THE   SPECIAL   SENSES 


335 


but  lies  loose  ill  ;i  direction  Jiloiij;'  the  canal.  The  layer 
of  this  ineini»iaii('  to  which  the  rods  and  hair-cells  are 
attached  is  stri[)cd  by  fibres  IVoni  side  to  side.  These 
fibres  difler  in  length,  the  shortest  being  at  the  base  of 


Fig.  152. — Diagram  of  a  section  of  the  membranous  cochlea,  j«how~ 
ing  position  and  arrangement  of  Corti's  organ,  i  and  e,  interior  and 
exterior  rods  of  Corti  ;  .1,  tunnel  formed  by  the  arching  rods  ;  //,  in- 
terior row  of  hair-cells;  //,  A,  A,  exterior  row  of  hair-celKs. 

the  cochlea,  and  the  longest  at  the  top.  The  length 
varies  from  about  .00162  inch  for  the  shortest  to  about 
.01949  inch  for  the  longest.  Thus,  the  latter  is  a  little 
more  than  twelve  times  the  former. 

Function  of  the  cochlea. — The  cochlea  alone  is 
the  organ  of  hearing.  All  sense  of  sound  and  music 
arises  in  the  cochlea. 

When  the  stapes  sets  up  a  vibratory  motion,  or  quiver, 
in  the  perilymph,  the  motion  is  easily  communicated  to 
the  delicate  membranes  about  the  membianous  cochlea, 


336  THIRD    BOOK   OF   PHYSIOLOGY 

aiul  tlie  eiidolyinph  partakes  uf  tlie  same  vi]>rations. 
The  fibres  of  tlie  basilar  membrane,  which  have  the 
proper  length  to  vibrate  in  sympathy,  will  be  most  agi- 
tated. The  rods  and  haii-cells  which  are  attached  to 
these  fibres  will  convej^  the  motion  to  the  terminals  of 
the  nerve-fibres. 

A  nervous  impulse  thus  started  will  travel  along  the 
auditory  nerve  to  the  medulla  oblongata  and  thence  by 
other  neurons  to  the  seat  of  perception  in  the  cerebrum. 

The  difference  in  the  length  of  the  fibres  of  the  basilar 
membrane  is  sufficient  to  explain  the  ear's  ability  to  dis- 
tinguish all  differences  of  pitch  in  music,  even  when  the 
difference  is  very  slight. 

The  ear  is  most  sensitive  in  the  first  octave  above 
middle  C.  Here  the  ear  of  some  trained  musicians  have 
been  able  to  distinguish  a  difference  of  one-half  a  wave 
per  second,  thus  making  about  1000  distinguishable  notes 
in  the  octave. 

Function  of  the  round  window. — Since  the 
whole  labyrinth  is  enclosed  in  a  hard,  bony  cavity  and  is 
filled  with  a  liquid  which  is  almost  incompressible,  it  is 
necessary  to  have  some  spot  which  will  yield.  The  pur- 
pose of  the  round  icbidow  is  to  yield  to  j)ressare  upon  the 
liquid  in  the  labyrinth.  ^Vhen  the  stapes  presses  in- 
ward, the  pressure  is  communicated  along  the  vestibular 
pa*ssage  of  the  cochlea  and  then  across  to  the  tympanic 
passage  and  down  to  the  oval  window,  which  is  thus 
made  to  bulge  out  into  the  tympanum  A  decrease  of 
pressure  in  the  labyrinth  would  cause  the  round  window 


TIIK   SPECIAL   SENSRS  337 

to  bnljxe  in.  The  oval  window  thus  permits  greater 
tVeedoiii  of  vibration  in  the  liquid. 

Function  of  the  semicircular    canals— The 

seniicircuhir  canals  and  vestibule  pr()bal)ly  liave  no  part 
in  produeiufj  the  seusation  of  hearing. 

The  position  and  structure  of  the  canals  as  well  as 
many  experiments  which  have  been  made  all  go  to  show 
tliat  their  function  is  to  give  a  sense  of  equilibnum.  'By 
this  sensation  it  is  possible  for  us  to  maintain  any  desired 
])osture  of  the  body.  The  least  tendency  to  fall  to  one 
side  or  the  other  is  at  once  made  known  and  checked  by 
the  use  of  the  proper  muscles. 

The  planes  of  the  three  canals  are  each  at  right  angles 
to  the  other  two,  and  hence  any  motion  of  the  head  will 
cause  a  motion  of  the  liquid  in  one  or  more  of  the  canals. 
This  motion  affects  the  auditory  hair-cells  to  which  the 
nerve-fibres  are  attached,  and  thus  a  nervous  impulse  is 
sent  on  the  vestibular  branch  of  the  auditory  nerve  to 
the  medulla  and  on  to  the  cerebellum. 

Experiments  made  with  birds  and  other  animals  show 
that  when  the  semicircular  canals  are  injured,  the  animal 
will  fall  from  side  to  side  when  it  attempts  to  move.  All 
sense  of  balance  and  ability  to  co-ordinate  muscular 
movement  appear  to  be  gone.  The  nerve  terminals 
in  the  vestibule  are  probably  associated  in  function  with 
those  of  the  semicircular  canals. 

Care  of  the  ear. — The  inner  ear  is  so  well  protected 
that  it  needs  no  care  except  in  so  far  as  it  shares  in  the 

22 


338  THIED   BOOK   OF   PHYSIOLOGY 

general  health  or  weakness  of  the  whole  system.  It  is, 
however,  capable  of  a  very  high  degree  of  culture  and 
refinement. 

A  great  deal  of  the  pleasure  and  enjoyment  of  this 
world  is  derived  from  music,  but  only  those  whose  ears 
and  minds  have  been  educated  to  that  which  is  best  in 
music  can  get  the  full  enjoyment  from  it. 

The  external  and  middle  ear  open  to  the  outside,  and 
so  can  receive  direct  care  at  our  hands. 

Sometimes  ear-wax  in  excess  will  gather  in  the  meatus 
or  collect  on  the  tympanic  membrane.  In  such  cases  it 
is  always  better  to  consult  a  i:)hysiciau,  for  the  attempt 
to  get  it  out  with  a  pinhead  or  other  hard  instrument 
may  cause  a  still  more  serious  injury. 

Insects  sometimes  get  into  the  meatus,  but  seldom  do 
any  injury.  A  little  warm  water  or  sweet  oil  poured  in 
will  usually  cause  them  to  come  out,  or  a  physician  can 
remove  them  with  proper  instruments. 

The  middle  ear  is  probably  the  greatest  source  of 
trouble  and  needs  our  greatest  care. 

When  the  throat  is  inflamed  and  sore,  thei-e  is 
always  danger  that  the  inflammation  may  be  com- 
municated to  the  Eustachian  tube  and  thence  into  the 
middle  ear. 

An  inflammation  of  the  linings  of  the  middle  ear  may 
cause  serious  illness  or  even  death.  Xot  only  the  middle 
ear  proper  may  be  affected,  but  also  the  mastoid  cells  in 
the  temporal  bone.  Here,  back  of  the  ear,  pus  may  col- 
lect where  there  is  only  a  very  thin  partition  of  bone 
between  it  and  the  brain.     In  that  case  it  may  be  neces- 


THE    ^^PECIAL    SENSES  330 

sary  t<>  l)ore  throiiirh  the  outer  layer  of  the  skull  Id  the 
pus  au(l  thus  drain  it  otY. 

CoUls  often  ''settle''  in  the  middle  ear  and  caust' a 
great  deal  of  pain  and  annoyance. 

sp:nse  of  touch 

Location  and  purpose  of  the  touch  organs.— 

The  whole  surface  of  the  skin,  and  the  mucous  membrane 
at  points  of  entrance  to  the  body,  are  covered  with 
minute  conical  elevations  called  the  papilla?.  These  are 
on  the  outer  surface  of  the  true  skin  and  are  covered  by 
the  epidermis.  In  some  regions  of  the  skin  the  papillie 
are  very  numerous,  and  on  the  palmar  surface  of  the 
hands  and  fingei*s  they  are  arranged  in  rows  which  can 
be  plainly  seen. 

Some  of  the  papillie  contain  only  loops  of  capillary 
blood-vessels  and  lymphatics,  but  othei*s  contain  a  special 
organ  called  the  tactile  corpuscle. 

The  purpose  of  the  tactile  corpuscle  is  to  give  us 
knowledge  by  contact  with  outside  bodies. 

The  eye  and  the  ear  are  the  two  great  organs,  of  about 
equal  importance,  through  which  we  gain  knowledge  bj^ 
means  of  waves  coming  from  the  objects  that  are  seen  or 
heard. 

The  sense  of  touch  is  third  in  importance. 

The  tactile  corpuscle. — Many  of  the  papilke  con- 
tain an  oval-shaped  body  called  the  tactile  coipuscle. 
These  are  found  on  the  palms  and  soles,  i>articularly  on 


340 


THIED    BOOK   OF   PHYSIOLOGY 


the  fiugers  and  toes,  where  about  one  out  of  every  five 
of  the  i^apillae  contains  this  organ.  One,  two,  or  three 
nerve- fibres  may  enter  directly  into  the  corpuscle  or 
after  winding  three  or  four  times  around  it. 

Other  tactile  end  organs  which  are  distributed  gener- 
ally in  the  skin  of  the  bod}'  are  the  end  bidbs.     These 


u  ^ 


Pig.  153. — Two  tactile  papillae  from  skin  of  finger.      Touch  corpuscle 
within  and  nerve-fibres  below. 

are  small  collections  of  epithelial  cells  to  which  nerve- 
fibres  are  connected.  They  are  quite  as  sensitive  as  the 
corpuscles  described  above. 


The  Pacinian  corpuscle. — The  Pacinian  cor- 
puscles are  small,  oval-shaped,  white  bodies  found  in 
many  parts  of  the  alveolar  tissue  beneath  the  skin.  They 
are  formed  of  thirty  or  more  tunics  of  connective  tissue 
and  contain  at  the  centre  a  terminal  of  a  nerve-fibre. 
Their  function  is  not  clearlv  understood. 


TIIK    SI»KCIAI>    Sl'^.NSES  341 

Sensitiveness  of  different  parts  of  the  body. — 
Ry  layin^!:  the  t\\<>  i)()iiits  of  ;i  compjiss  upon  the  skin  at 
various  i)laees,  a  test  can  easily  be  made  of  one's  ability 
to  distin<rnish  two  points  of  contact.  By  bringing  the 
points  of  the  compass  closer  and  closer  together,  a  dis- 
tance will  be  reached  where  the  two  points  are  judged 
}is  one.  This,  then,  is  a  test  of  the  closeness  and  delicacy 
of  the  tactile  organs. 


Fig.  lo-i. — Two  Pacinian  corpuscles.      (Microphotograph.) 

The  place  where  the  two  points  may  be  most  nearly 
together,  and  yet  be  felt  as  two,  is  on  the  tip  of  the 
tongue.  The  place  of  least  sensitiveness  is  in  the  middle 
of  the  back.  Some  of  these  tests  show  that  this  dis- 
tance on  the  tip  of  the  tongue  is  about  2V  of  an  inch  ; 
on  the  end  of  the  finger  about  tV  inch  ;  on  the  lip,  I  inch  : 
on  the  forehead,  nearlj^  one  inch  ;  and  on  the  upper  arm 
and  back,  about  two  inches. 


342  THIED   BOOK   OF   PHYSIOLOGY 

Path  of  the  nervous  impulse.— The  nervous 
impulses  resulting  from  touch  are  carried  chiefly  by  the 
sensory  fibres  of  the  spinal  nerves  to  the  spinal  cord. 
There  a  reflex  action  may  occur  and  a  motor  impulse  be 
at  once  sent  out.  This  happens  when  the  touch  is  such 
as  to  indicate  an  injury  of  the  part  touched. 

At  the  same  time  the  sensory  impulse  is  carried  by 
other  neurons  to  the  proper  centre  in  the  cortex  of  the 
cerebrum.  There  not  only  do  we  perceive  that  the  body 
has  been  touched,  but  the  point  is  exactly  located,  and 
other  motor  impulses  may  be  sent  out  from  that  centre. 

Training  of  the  sense  organs. — The  organs  of 
touch,  particularly  those  in  the  ends  of  the  fingers, 
are  capable  of  training,  so  that  they  will  be  a  valuable 
means  of  gaining  information  in  regard  to  outside  objects. 
The  sense  of  touch  may  be  more  reliable  than  any  of  the 
other  senses,  as  in  judging  the  shape  and  surface  of  ob- 
jects, or  the  texture  of  fabrics.  One  who  is  blind  soon 
learns  to  read  by  moving  the  fingers  along  a  row  of  raised 
letters,  and  can  quicklj^  recognize  a  friend  by  passing  the 
hand  over  the  face. 

Miss  Helen  Keller  has  not  been  able  to  see  or  hear 
since  she  was  two  years  old,  and  yet  she  has  been  able, 
through  the  sense  of  touch,  to  become  highly  educated. 

SENSE    OF   SMELE 

The  nose. — The  sense  of  smell  is  located  in  the  nose. 
The  large  cavity  in  the  skull,  between  the  two  orbits  of 
the  eyes,  is  occupied  by  the  nasal  passages.     The  cavity 


THE   SPECIAL   SENSES 


343 


is  divided  into  two  coinpartiiients  by  ii  i)iirtitioii  whidiis 
bone  ill  the  posterior  i>iut,  but  is  continued  us  cartilage 
towards  the  end  of  the  nose. 

Iloth  passages  open  freely  to  the  air  in  front  and  to  the 
l)harynx  in  the  rear.  Both  passages  are  covered  with 
mucous  membrane,  a  large  surface  being  presented  not 


T 


Fig.   loo. — o,  olfactory  })ulb  ;     ?i,   nerves  descondirif;   to   the  mucous 

membrane. 


onlj^  by  the  i)lain  walls,  but  also  by  the  three  turbinated 
bones  which  x)roject  from  the  exterior  sides  of  the  nostrils 
The  lower  j)art  of  the  nose  cavity  is  called  the  I'esjnra- 
tory  region^  for  it  is  properly  fitted  for  receiving  air  into 
the  body,  as  has  been  exi)lained  under  the  subject  of 
respiration.  Here  the  lining  membrane  is  composed  of 
ciliated  ei^ithelium.  The  upper  part  of  the  cavity  is 
called  the  olfactory  region. 


344  THIRD    B(30K    OF   PHYSIOLOGY 

The  olfactory  region. — In  the  upper  part  of  the 
Dostrils  the  organ  of  smell  is  located.  Here  the  surface 
is  also  covered  with  epithelial  cells,  but  they  are  not 
ciliated  and  their  construction  is  peculiar.  Part  of  them 
contain  an  oval  nucleus  from  which  long  projections  ex- 
tend on  each  end,  one  coming  to  the  surface  of  the  mem- 
brane and  the  other  extending  back  to  a  nerve-fibre. 
Numerous  cells  of  this  kind  reach  the  free  surface  of  the 
mucous  membrane  at  one  end,  and  connect  with  a  nerve- 
fibre  at  the  other. 

Xumerous  glands  in  this  region  keep  the  surface  con- 
stantly moist. 

The  act  of  smeHing. — Odors  which  arise  from 
substances  are  carried  in  the  air.  In  ordinary  breathing, 
a  small  area  of  the  olfactory  region  is  always  exposed  to 
the  air  passing  through  the  nostrils,  but  by  '^sniffing," 
the  air  is  admitted  to  a  much  larger  area  and  many  more 
of  the  nerves  of  smell  are  affected. 

The  fine  x>articles  suspended  in  the  air  must  fall  ux^on 
the  moist  mucous  membrane  and  be  dissolved,  or,  if  a  gas, 
must  enter  into  solution  before  they  produce  any  effect. 

An  impulse  started  by  this  stimulus  will  travel  to  the 
olfactory  bulbs,  as  shown  in  Fig.  155,  and  will  there  be 
taken  up  by  other  neurons  and  carried  to  the  seat  of  per- 
ception in  the  temporal  lobes  of  the  cerebrum. 

The  use  of  the  smelling  sense. — In  many  of  the 
lower  animals,  as  in  certain  breeds  of  dogs,  the  sense  of 
smell  is  the  most  important  of  the  five  senses. 


TIM-:    SIM-^CIAL    SENSKS  345 

In  man  tliis  sense  is  nflen  uiuleresti mated.  Tlie  pri- 
mary purpose  is  to  j^ive  us  knowledge  of  any  liarmful 
substance  in  the  air  wliich  we  ))reathe.  As  a  secondary 
use,  it  enables  us  to  distinguish  objects  by  their  odor,  and 
to  give  pleasui-e  in  the  presence  of  pleasjint  odors.  Tlie 
impressions  made  by  the  sense  of  smell  appear  to  l)e 
very  distinct  and  lasting. 

When  the  same  odor  is  breathed  through  the  nostrils 
for  a  time,  it  ceases  to  aifect  the  organ  of  smell.  When 
one  comes  from  fresh  air  into  a  close  room,  the  bad  con- 
dition of  the  air  is  very  noticeable  at  first,  but  after  a 
few  breaths  the  ability  to  distinguish  the  foul  from  the 
pure  air  is  lost,  until  a  change  of  air  is  again  made. 
The  air  in  Mammoth  Cave  is  quite  free  from  the  float- 
ing particles  which  are  plentiful  in  the  air  we  ordi- 
narily breathe.  After  a  few  hours  in  the  cave,  one  will, 
on  coming  out  into  the  air  again,  feel  a  keen  pain  in  the 
nostrils  until  he  becomes  accustomed  to  the  outside  air. 

Since  the  mucous  membrane  of  the  nostrils  is  the  first 
to  be  exposed  to  the  air  which  we  inhale,  it  will  intercept 
most  of  the  i^articles  which  are  floating  in  the  air,  and 
thus  it  is  often  irritated  and  inflamed,  and  a  catarrhal 
condition  is  brought  about,  which  is  very  destructive  to 
the  organ  of  smell. 

THE   SENSE   OF   TASTE 

Location  and  structure  of  the  organs  of 
taste. — Just  as  the  organ  of  smell  is  a  guard  at  the  gate- 
way to  the  lungs,  so  the  organ  of  taste  is  a  guard  at  the 
gateway  to  the  stomach. 


34G 


THIRD    BOOK    OF   PHYSIOLOGY 


A  ^^^ 


si 


•13 


Fig.  156. — View  of  the  dorsum  of  the  tongue.  1,  2,  Y-like  row 
of  the  circumvallate  papilhie ;  3,  fungiform  papiUae ;  4,  5,  conical 
papilUe ;  6,  6,  floor  of  the  fauces,  with  numerous  lymphoid  follicular 
glands  ;   7,  tonsils  ;  8,  summit  of  the  epiglottis. 


TIIK    SPK(^IAIi    SKNSKS 


347 


The  organs  of  taste  are  found  in  various  parts  of  the 
mouth,  but  chiefly  on  the  palate  and  tonjj^ue.  On  the 
ton<;^ue  numerous  little  eminences  may  be  plainly  seen 
with  the  naked  eye.  These  are  papilke,  wliich  contain 
the  organs  of  tiiste.  On  the  frout  part  of  the  tongue 
there  are  small  conical  projections  called  filiform  papilhv. 
On  the  middle  region  they  are  larger  and  appear  like  a 
fungus  growth,  and  so  are  called  fungiform  papillw.     On 


Fig.  157. — Cross-section  of  a  circumvallate  papilla,     f^  taste-buds;  i/>, 
wall ;  g^  nerve-fibres  connected  to  taste-buds. 


the  back  of  the  tongue  are  eight  or  ten  large  elevations 
arranged  in  a  V  form  with  the  vertex  of  the  V  towards  the 
throat.  Each  of  these  appears  to  be  surrounded  wath  a 
ditch  and  a  w^all,  and  so  are  called  cireumvaUate  papillce. 

Within  the  latter  two  kinds  of  papillae  are  clusters  of 
cells  called  taste-huds.  Within  the  buds  are  several  cells 
which  i:)roject  from  the  end  of  the  bud,  and  to  which 
fibres  of  nerves  are  attached.     These  are  the  taste-cells. 

These  buds  are  arranged  in  the  sides  of  the  depressions 


348  THIRD   BOOK    OF   PHYSIOLOGY 

around  the  circumvallate  papillae  as  shown  in  Fig.  157. 
Thej^  are  also  found  in  the  fungiform  papillae. 

Conditions  and  kinds  of  taste. — A  substance 
must  be  in  solution  before  it  can  affect  the  taste-cells. 
If  the  tip  of  the  tongue  he  wiped  dry  and  some  dry 
sugar  be  touched  to  it,  no  taste  will  follow  until  the  tongue 
again  becomes  moist.  By  the  sense  of  taste  it  is  possible 
to  distinguish  sweet,  sour,  bitter,  and  salt. 

The  tip  of  the  tongue  is  best  adapted  for  receiving  a 
stimulus  from  sweet  substances,  and  the  sides  and  back 
of  the  tongue  for  sour  or  bitter  substances. 

Cultivation  of  taste. — By  proper  attention  the 
sense  of  taste  may  be  made  very  acute.  Some  persons 
are  i^aid  good  salaries  for  doing  nothing  but  determine 
the  quality  of  liquors  by  their  cultivated  sense  of  taste. 
The  constant  use  of  tobacco  and  alcoholic  liquors  will, 
however,  so  blunt  this  sense  that  most  substances  will 
have  no  taste  or  will  all  taste  alike. 

Smell  and  taste  are  closely  associated  and  often  con- 
fused. The  odor  from  substances  in  the  mouth  may 
easily  pass  up.  from  the  throat  into  the  nostrils,  and 
thus  we  attribute  to  the  sense  of  taste  what  belongs  to 
the  sense  of  smell.  If  while  eating  an  onion  the  nostrils 
be  held  shut,  the  so-called  onion  taste  will  not  be  per- 
ceived. 


TlIK    SPECIAL    SKXSKS  349 

QT^ESTIONS  FOR  KEVIKW. 

1.  "Wliat  are  the  special  senses? 

2.  Name  and  describe  five  general  senses. 

3.  "What  is  the  great  advantage  of  the  five  special  senses? 

4.  What  are  the  two  great  media  through  which  stimuli  reach 
the  special  senses, — the  eye  and  the  ear? 

5.  Make  a  sketch  and  locate  the  parts  of  the  eye. 

6.  "What  is  the  use  of  the  front  parts  of  the  eye? 

7.  Describe  the  cornea. 

8.  When  is  light  refracted? 

9.  ^lake  a  drawing  to  show  how  rays  of  light  are  affected  by 
the  cornea. 

10.  Describe  the  iris. 

11.  What  is  the  use  of  the  iris? 

12.  Describe  the  crystalline  lens. 

13.  What  is  the  chief  use  of  the  lens? 

14.  Explain  how  the  convexity  of  the  lens  is  changed  for  dif- 
ferent distances . 

15.  AVhen  is  the  eye  emmetropic? 

10.  Explain  the  condition  of  the  myopic  eye. 

17.  When  is  the  eye  said  to  be  hypermetropic? 

18.  What  kind  of  glasses  must  be  used  for  near-sighted  or  far- 
sighted  eyes  ?    Why  ? 

19.  How  is  the  eye  moved? 

20.  Explain  the  cause  of  cross-eyes. 

21.  What  is  the  function  of  the  posterior  parts  of  the  eye? 

22.  What  are  the  three  coats  of  the  eye?    Which  is  most  essen- 
tial?    Why? 

23.  Describe  the  retina. 

24.  AVhat  are  the  rods  and  cones,  and  where  are  they  placed  ? 

25.  Locate  and  describe  the  yellow  spot. 

26.  Where  is  the  blind  spot  ? 

27.  AVhat  is  the  size  of  the  image  on  the  retina? 


350  THIRD   BOOK   OF   PHYSIOLOGY 

28.  How  close  can  two  points  be  together  and  still  be  seen  as  two  ? 

29.  Describe  the  optic  nerve. 

30.  How  are  two  eyes  better  than  one  ? 

31.  Explain  the  perception  of  color. 

32.  Explain  all  the  ways  by  which  the  eyes  are  protected. 

33.  What  care  should  be  taken  of  the  eyes  ? 

34.  How  do  alcohol  and  tobacco  injure  the  eyes  ? 

35.  Explain  the  nature  of  air-waves. 

36.  How  fast  does  sound  travel  ?    Light  ? 

37.  AVhat  are  the  three  parts  of  the  ear  ? 

38.  Describe  the  pinna  and  give  its  use. 

39.  Describe  the  meatus. 

40.  Why  is  the  middle  ear  called  a  drum  ? 

41.  Xame  the  parts  of  the  drum. 

42.  Describe  the  structure  and  use  of  the  tympanum. 

43.  Make  a  drawing  of  the  three  bones  and  describe  them. 

44.  How  do  the  bones  increase  the  force  of  the  vibrations  ? 

45.  What  is  tlie  use  of  the  Eustachian  tube? 

46.  What  are  the  openings  into  the  drum  ? 

47.  How  large  is  the  drum  ? 

48.  Where  is  the  labyrinth  located,  and  what  are  its  three  parts? 

49.  Describe  the  osseous  labyrinth. 

50.  Describe  the  membranous  labyrinth. 

51.  How  do  the  nerves  end  in  the  utricle,  saccule,  and  semi- 
circular canals  ? 

52.  Describe  the  membranous  cochlea. 

53.  Give  a  full  description  of  the  oi^an  of  Corti. 

54.  What  is  the  function  of  the  cochlea  ? 

55.  Of  what  use  is  the  round  window? 

56.  What  is  the  function  of  the  semicircular  canals? 

57.  How  can  the  ear  be  properly  cared  for  ? 

58.  Wliere  are  the  organs  of  touch  located  ? 

59.  Describe  a  tactile  corpuscle. 

60.  What  is  a  Pacinian  corpuscle  ? 


THE   SPF.CIAL   SENSES  351 

61.  What  part  <>f  i\w  body  \n  most  sensitive  to  touch?     Wliat 
least?     HoNv  can  this  be  determined? 

62.  How  do  we  know  wlien  we  are  touched? 

63.  Describe  the  structure  of  the  nostrils. 

64.  Explain  the  use  of  "sniffing." 

66.  Of  what  advantage  is  a  keen  sense  of  smell? 

66.  Where  are  the  organs  of  taste  located? 

67.  Describe  the  taste-buds. 

68.  What  are  the  four  taste  sensations? 

69.  How  are  smell  and  taste  confused? 

70.  Which   of  the  special   senses  do  you  prize   most   highly? 
Why? 

EXPERIMENTS. 

1.  Secure  at  the  butcher-shop  two  or  three  eyes  of  the  ox  or  sheep.  Closely 
examine  one  of  them,  noting  the  tough,  white  sclerotic  coat  on  the  outside;  the 
point  of  entrance  of  the  optic  nerve ;  the  bulging,  transparent  cornea  on  the 
front ;  the  iris  and  pupil  beneath.  Cut  through  the  cornea,  noting  its  thickness 
and  the  limpid  aqueous  humor  within.  Find  the  crystalline  lens  and  notice 
the  curvature  of  its  two  sides.  Open  the  back  part,  noting  the  three  coats  and 
the  thick  vitreous  humor  within. 

2.  Hold  a  mirror  close  before  the  face  and  notice  the  size  of  the  pupil. 
Shade  the  eyes  from  the  light,  and  the  iris  can  be  seen  to  draw  back  on  all 
sides,  thus  making  the  pupil  larger.  Suddenly  admit  more  light  to  the  eyes 
and  the  pupil  will  grow  smaller. 

3.  Make  on  a  piece  of  white  paper  two  black  spots  about  three  inches 
apart.  Hold  the  left  eye  shut  and  look  with  the  right  eye  steadily  at  the  spot  on 
the  left.  By  varying  the  distance  a  position  of  the  paper  can  ea,sily  be  found 
■where  the  image  of  the  spot  on  the  right  side  will  fall  upon  the  place  where  the 
optic  nerve  enters  the  right  eye.  This  is  the  blind  spot,  and  so  the  image  makes 
no  impression,  that  is,  cannot  be  seen. 

A.  Try  to  see  a  whole  line  of  this  jjage  distinctly  without  moving  the  eyes. 
Try  a  single  small  word.  Try  a  single  letter.  Only  the  images  of  very  small 
objects  can  be  wholly  contained  in  the  yellow  spot.  Hence  the  need  of  many 
muscles  to  freely  move  the  eyes  from  point  to  point. 

5.  Use  a  pocket  microscope  as  a  len.s.    Hold  it  near  the  wall  of  a  room  and 


352  THIRD    BOOK    OF   PHYSIOLOGY 

note  the  image  of  a  window  or  burning  lamp.    This  is  the  action  of  the  eomea 
of  the  eye. 

().  Look  through  a  window  and  adjust  the  crystalline  lens  so  that  some 
object,  as  a  tree  or  a  house,  can  be  seen  distinctly.  At  the  same  time  the 
window  can  be  seen,  but  only  indistinctly.  Now  readjust  the  lens  so  that  the 
window  can  be  distinctly  seen,  and  then  the  objects  beyond  can  be  seen  only 
indistinctly. 

7.  The  image  on  the  retina  of  an  eye  may  be  seen  by  cutting  away  the  two 
outside  coats  from  the  back  of  the  eye  of  an  ox.  The  thin  retina  must  be  care- 
fully left  in  place.  If  the  eye  thus  prepared  be  now  pointed  towards  a  candle 
or  lamp,  and  the  light  be  screened  from  the  eyes  of  the  observer,  an  inverted 
image  can  be  seen  on  the  retina. 

8.  Rapidly  rotate  a  wheel  and  notice  that  the  spokes  will  all  apparently  be 
blended.  The  space  between  the  spokes  and  the  spokes  themselves  unite  to 
form  a  transparent  disc.  This  is  because  a  retinal  impression  lasts  for  about 
one-seventh  of  a  second.     If  the  rotating  wheel  is  seen  by  the  light  from  a 

stroke  of  lightning,  it  will  appear  to  be  standing  still. 

9.  Prepare  two  discs  of  card-board,  about  six  inches  in  diameter,  one  blue 
and  the  other  yellow.  Hold  the  blue  one  against  a  white  background  and 
look  steadily  at  it  for  a  minute,  then  suddenly  jerk  it  away.  A  yellow  disc  will 
be  seen  in  its  place.  Try  the  same  with  the  yellow  one,  and  a  blue  outline  of 
the  disc  will  appear  on  the  white  background. 

These  are  two  complementary  colors  and  will  when  mixed  produce  white. 
When  the  eye  was  fatigued  by  looking  at  the  yellow  it  was  still  sensitive  to  its 
complement, — the  blue.  When  it  was  fatigued  by  the  blue  it  could  more  dis- 
tinctly see  the  yellow. 

10.  Close  the  nose  and  mouth  and  blow  air  through  the  Eustachian  tube  into 
the  ear-drum.    Notice  that  hearing  is  then  less  distinct. 

11.  Utter  quick,  explosive  notes  into  a  piano  and  notice  how  it  returns  the 
same  note  whatever  the  pitch  may  be.  By  this  illustrate  the  sympathetic  action 
of  the  fibres  in  the  basilar  membrane  of  the  cochlea. 

12.  Use  a  compass  with  blunt  points  and  try  on  various  parts  of  the  body 
how  close  together  the  points  may  be  and  yet  be  felt  as  two  points. 

18.  It  is  an  interesting  test  of  one's  ability  to  locate  the  spot  where  he  has 
been  touched,  if  one  will  close  his  eyes  while  another  touches  him  with  the 


THE   SPECIAL   SENSES  353 

point  of  11  pencil.    Then  sec  how  nearly  the  one  who  is  touched  can  locate  the 
exact  spot. 

U.  Cn)s.s  two  finpers  and  roll  a  hullet  or  small  naind  body  between  them. 
One  will  appear  as  two. 

1;').  I'hu-e  the  .same  numljer  of  shot  in  each  of  two  bottles.  Balance  one 
lK)ttk'  in  each  hand  to  determine,  by  the  mn.scnlar  .sen.se,  the  weij^ht.  Then 
have  some  one  change  a  few  siiot  from  one  bottle  to  the  other  and  then  try  to 
determine  which  bottle  is  the  heavier.  By  continued  practice  the  rau.scular 
sense  becomes  very  acute. 

1().  Prepare  three  vessels  of  water.  One  hot,  one  cold,  and  a  third  luke- 
warm. Place  one  hand  in  the  hot  water  and  the  other  in  the  cold.  After  a 
short  time  transfer  both  to  the  lukewarm  water,  and  it  will  feel  cold  to  the  hand 
that  was  in  the  not  water,  and  warm  to  the  hand  that  was  in  the  cold  water. 


£3 


GLOSSARY 


A  LIST  of  physiological  ternjs  likely  to  be  mispronounced. 

It  is  a  good  plan  to  have  the  class  pronounce  this  list  of  words 
occasionally  until  the  pupils  become  accustomed  to  the  sounds  and 
accents. 


Ab  do'men 

Ad'i  pose  (ad'i  pos) 

Af'fer  ent 

Al  bu'meu 

Al  ex'ines  (al  eks'ins) 

Al  i  men'ta  ry 

A  mci/ba  (a  me  ba) 

Am  phib'i  a  (am  fib'e  ah) 

A  nat'o  my 

An  ti  tox'in  (an  te  lok'sin) 

A  or'ia 

Ap  pen  di  ci'tis 

A 'que  ous  (a'kwe  us) 

Ar  ach'noid  (ar  ak'noid) 

Ar  e'o  lar 

Ar'ter  y 

Ar  tic'u  lar 

Au'di  to  ry 

Au'ri  cle  (aw'rik  1) 

Au  ric'u  lo  ven  tric'u  lar 

Bac  te'ri  a 
Bac  te  ri  ol'o  gy 
Bas'i  lar 
Bi'ceps  (bi'seps) 
Bi  cus'pids 
Bron'chi  (bron'ki) 


Cae'cum  (se'kum) 

Cal'o  rie  (kal'o  re) 

Can  al  ic'u  li 

Can'cel  lous 

Ca' nines 

Cap'il  la  ries 

Car  bo  hy'drates 

Car'di  ac 

Car  ti  lag'in  ous  (g  =  j) 

Ca  tarrh'al 

Cen'tral  fo'vea  (fo've  ah) 

Cer  e  bel'lum 

Cer'e  bro  spi'nal 

Cer'e  bro  spi'nal  men  in  gi'tis 

(Ser'e  bro  spi'nal  men  in  ji'tis) 

Cer'e  brum  (ser'e  brum) 

Cer'vi  cal  (ser'vi  kal) 

Cho'roid  (ko'roid) 

Chro'ma  tin  (kro'mat  in) 

Chyle  (kii; 

Chyme  (kim) 

Cil'i  a  ted 

Cir'cum  val'late 

Co  ag  u  la'tion 

Coc'cyx  (kok'six) 

Coch'lea  (kok'leah) 

Con'cha  (kong^kah) 

355 


356 


GLOSSAEY 


Cor'ne  a  (kor'neah) 
Cor'pus  cal  lo'sum 
Cor'pus  cle 
Cra'ni  um 
Crys'tal  line 
Cy  clo  slo'ma  la 

Deg  lu  ti'tion 

De  lir'i  um  tre'mens 

Den'drites 

Den'tiue  (den'tin) 

Di'a  phragni  (di'af  ram ) 

Diph  the'ri  a  (dif  the're  ah) 

Dip  soma'ni  a 

Dis  sec'tion 

Du  0  de'num 

Du'ra  ma'ter 

Ef'fer  ent 

E  lee  trol'y  sis 

Em  me  trop'ic 

E  mul'si  fied 

En  am'el 

En  do  car'di  um 

En'do  lymph  (en'do  limi) 

En  dos'te  um 

En  vi'ron  ment 

Ep  i  glot'tis 

Ep  i  the'li  um 

E  qui  lib'ri  um 

Er'go  graph 

Eu  sta'chi  an  ( u  sta'ke  an) 

E  vap  o  ra'tion 

Ex' ere  to  ry 

Ex  ha  la'tion 

Fah'ren  heit  (Fah'ren  hit) 
Fas  cise  (fash'e  e) 
Fas  cic'u  li  ( fas  ik'u  li) 
Fau'ces  ( law'sez) 
Fer  men  ta'tion 


Fi  brin'o  gen 

Fib'u  la 

Fil'i  form 

Fis'sure  (fish'ur) 

Flagei'la(fla  jel'la) 

Fo  ra'men 

Fun'gi  form  (.fun'ji  form) 

Gan'gli  a  (gang'gle  a) 
Gly'co  gen  (gli'ko  jen) 
Gus'ta  to  ry 
Gym  na'si  a 

Ha  ver'si  an  ( Ha  ver'zhan  ) 

Hem  o  glo'bin 

Hi'lum 

Hy  dro  chlo'ric 

Hy  dro  pho'bia 

Hy'gi  ene 

Hy  per  me  trop'ic 

Hy  po  gas'tric 

II  e  o  col'ic 

Il'e  um 

In  ci'sors 

In'cus  (ing'kus) 

In  fun  dib'u  la 

In  ha  la'tiou 

In  nom  i  ua'tum 

In  sal  1  va'tion 

In  som'ni  a 

In  ter  cos'tal 

In  tes'tine  (in  tes'tin) 

In  Torun  ta  ry 

Je  ju'num 

Ki  net'ic 

Lab'y  rinth 

Lach'ry  mal  ( lak'rim  al ) 


GLOSSARY 


357 


Lac'te  al 

Lar'ynx  ( 'ar'ingx) 

Lie'ber  kuhn  (le'ber  k6n) 

Lo'cal  i  /a'tion 

Ln'mi  la 

Lym  phat'ics  (lim  fat'ics) 

Mag  ne'si  urn 

Mal'le  us 

Mai  pig'hi  an  (nial  pig'e  an) 

Mas  li  ca'tion 

Mas'toid 

Max'il  la  ry 

Mo  a'tus 

Me  (lul'la 

Me  dul'la    ob  Ion  ga'ta 

Med'ul  la  ry 

Mem'bra  nous 

Men  in'ges  (men  in'jez) 

Mes'en  te  ry 

Met  a  ear' pal 

Met  a  tar'sal 

Mi  cro  pho'to  graph 

Mi  cro  scop'ic 

Mo  di'olus 

Mor'phine  ( mor'fin ) 

Mu'cous  (mu'kus) 

Mu  riat'ic 

My  op'ic 

My'o  sin 

Neu'ron 

Nic'o  tine  (nic'o  tin) 

Nu'cle  us 

Oc  cip'i  tal 

0  don'toid 

Oe  soph'a  gus  (e  sof  a  gus) 

01  fac'to  ry 
Os  mo'sis 

Os'se  ous(os'e  us) 


Os'si  cle  (os'e  kl) 
5'to  lith 
Ox  i  (la'tion 

Pa  cin'i  an 

Pan'cre  as 

Pa  i)il'la)  (03  =  e) 

Par'a  lyzed 

Pa  ri'e  tal 

I'a  roL'id 

I'a  tel'la 

Per  i  ear'di  um 

Per'i  lyiuph 

Per  i  os'te  um 

Per  i  star  tic 

Per  i  to  ne'um 

Per  spi  ra'tion 

Pha  lan'ges  (fa  lan'jez) 

Phar'ynx  (far'inx) 

Phos'pho  rus  ( fos'fo  rus) 

Phys  i  ol'o  gy 

Pi'a  ma'ter 

Pleu'ra  (plu'rah) 

Pneu  mo  gas' trie  (nu  mo  gas'tric) 

Pneu  mo'ni  a  (nu  mo'ne  ah) 

Po  tas'si  um 

Po  teu'tial  ( po  ten'shal ) 

Pro'te  id 

Pro'to  plasm 

Pro  to  zo'a 

Pty'a  iin  ( ti'a  lin ) 

Pul'mo  na  ry 

Py  lo'rus 

Rac'e  mose  (ras'e  mos) 
Re  frac'tion 
Res'pi  ra'tion 
Res' pi  ra  to  ry 
Ret'i  na 

Sac'cule 

Sar  CO  lem'ma 


358 


GLOSSAEY 


Scle  rot'ic  (skle  rot'ic) 

Se  cre'tion 

Sem  i  cir'cu  lar 

Sem  i  lu'nar 

Se'rous  (se'rus) 

Skel'e  tal 

Sta'pes  ( sta'pez ) 

Sto'ma  ta 

Stri'a  ted 

Sub  cla'vi  an  (sub  kla've  an) 

Sub  lin'gual  (sub  ling'gwal) 

Sub  max'il  la  ry 

Sul  phu'ric 

Su'ture 

Sym  pa  tbet'ic 

Syn  o'vi  al 

Tet'a  nus 

Tho  rac'ic  (tho  ras'ic) 

Tib'ia 

Tis'sue  (tish'u) 

Tra'che  a  ( tra'ke  ah) 


Trans  pi  ra'tion 
Tri  chi'n£E  (triki'ne) 
Tu  ber  cu  lo'sis 
Tym'pan  um 
Ty'phoid 

Un  du  la'tions 
U  re'a  (u  re'ah) 
U  rin  if'er  ous 
U'vu  la 


Vac'u  um 

Val'vu  Ise  con  ni  ven'tes 

Vas  o  mo' tor 

Ven'tri  cle 

Ver'te  bra  (plural  se  =  e) 

Ves'ti  bule 

Vil'li 

Vil'lus 

Vit're  ous 

Vol'un  ta  ry 


INDEX 


Abdomen,  30 

Adam's  apple,  166 

Adipose  tissue,  26 

Afferent   nerves,  245 

Air,   162,   163,  295 

composition  of,   174 
germs  in,  1S5 
quantity  breathed,  174 
waves  of,  320 

Alcohol 

and  oxygen,   158 
as  a  food,  91,  92 
as  a  mental  stimulus,  284 
effect  on  muscle,  74 
effect  on  digestion,  114 
effect  on  circulation,  157,  158 
effect  on  respiration,  186 
effect  on  kidneys,  229 
effect  on  the  nervous   sys- 
tem, 281 
effect  on  eye.  319 
excessive  use  of.  2S5 
hereditary  effect,  287 
quantity  in  drinks.  123 
small  doses  of,  283 

Alexines,  202 

Alimentary  canal,  96 

Amneba.  21 

Anatomy,  9 

Animals  and  vegetables,  6 

Antitoxin,  198 

Aorta.  134 

Appendicitis,  112 

Arachnoid,  238 


Argon,   176 
Arteries,  136 
Atlas,  39 
Auricles,  132 
Auriculo-ventricular   valves, 

133 
■Axis,  40 
Axis-cylinder,  234 

B 

Bacteria,  192 

food  of,  194 

use  of,   195 
Ball-and-socket  joint,  56 
Basilar  membrane,  333 
Bathing,  216 
Beating  of  heart,  153 
Biceps,  61 
Bicuspids,   98 
Bile,  110 

action  of.   Ill 
Bleeding,  156 
Blind  spot.  311 
Blood 

composition  of,  142 

experiments  on,   161 

function  of,  142 

quantity  of,  142 
Blood-clots.  145 
Blood-plasma,  142 
Blushing,  150 
Bone,  33 

classes  of,  36 

composition  of,  47 

experiments  on,  52 

359 


560 


i:NrDEX 


Bone,   fracture  of.   oO 

health   of,    48 

microscopic  appearance,  46 

names  of,  35 

nourishment  of,  47 

number  of,  33 

of  ear,  325 

strength  of,  45 

use  of,  33 
Brain,  238 

a  favored  organ,  272 

convolutions  of,  242 

lobes  of,  241 

parts  of,  239 

supply  of  blood  to,  274 

weiglit  of,  239,  262 
Bright's  disease,  229 
Bronchi,    167 
Bronchial   tubes,    169 


Caecum,  112 
Canaliculi,  46 
Cancellous  bone  tissue,  45 
Canines,  98 
Capillaries,  137 
Carbohydrates,  84,  86 
Carbon  dioxide,  176 
Cardiac  orifice,  102 
Carotid  artery,  274 
Cartilage,  27 
Cells,   13 

division  of,  19 

how  formed,  19 

origin  of,  16 

parts  of,   17 
Centrosome,  19 
Cerebellum,  242 

function  of,  262 
Cerebrospinal   meningitis,   239 
Cerebrum,  240 


Cerebrum,  function  of,  259 

Cholera  infantum,  197 

Chromatin,  18 

Chyle,    111 

Chyme,  105 

Cilia,  25 

Circulation,  128 

effect  of  exercise  on,  155 

hygiene  of,    155 

organs  of,   130 

scheme  of,   148 

systems  of,   149 
Circumvallate  papillse,  347 
Coagulation,   146 
Coccyx,  40 
Cochlea,  330,  335 
Colds,  156 

Color  sensations,  315 
Composition  of  body,   33,   34 
Cones,  311 
Conjunctiva,  318 
Connective   tissue,    25 
Convolutions  of  brain,  242 
Corn,  87 

Cornea,    297,  298 
Corpus  eallosum,  240 
Cortex  of  cerebrum,  241 
Cortex  of  kidney,  226 
Corti's  arches,  335. 
Cranial  nerves,  246 
Cranium,  38 
Cross-eyes,  309 
Crystalline  lens,   302 

D 

Deglutition,   102 
Delirium  tremens,  286 
Dendrites,  234 
Dentine,  99 
Dermis,  208 
Diaphragm,  30 


IN1)P]X 


36^ 


]  )i:;-c'stioii,  9.") 

experiments  on,  117 
in  intestines,  110 
in  stomach,   104 
organs  of,  07 
why  necessary,  95 

Diphtheria,   107 

Drum  of  ear,  323 

Duodenum,    lOG 

Dura  mater,  238 

Dust  in  air,  184 

E 
Ear,  321 

anatomy  of,  322 

care  of,   337 
p]fFerent  nerves,  245 
Emmetropic  eye,  305 
Enamel,  00 
Endolymph,   331 
Endosteum,  47 
End  plates,  252 
Energy,  80,  81 
]]pidermis,   207 
Epiglottis,  101,  166 
Epithelium,   24 
Ether,  295 

Eustachian  tube,  326 
Excretions,  221 

organs  of,  222 
Exercise,  71 
Exhalation,  173 
External  ear,  322 
Eye,  296 

anatomy  of,  296 

care  of,  318 

protection  of,  316 


Fascia,  67 
Fasciculi,  67 


Fat,   84 
Fatigue,  275 
Fauces,   101 

Fermentation,   197 
I'ihres  of  musch',  67 
Fihrin,   145 
Fibrinogen,   14o 
Flat  bones,  37 
Food,  79 

a  complex  compound,  85 

amount  of,   89 

compared  to  coal  in  engine, 
81 

cooking  of,   90 

definition  of,  85 

for  brain,  273 

mixed,   88 

produced   by   bacteria,    196 


Gall-bladder,  110 
Ganglia,  233 
Gastric  gland,  104 

juice,  104 
General  sensations,  293 
Germs  in  air,  185 
Glands,  29 
Gliding  joint,  57 
Glycogen,  129 
Gout,  57 

H 

Habit,  268,  280 
Hair,  212 

care  of,  218 
Haversian  canals,  46 
Health,  204 
Heart,  130 

divisions  of,   132 

valves  of,  132 

work  of,  154 


362 


IXDEX 


Hemispheres  of  brain,  240 
Hemoglobin,   144 
Hilum,  224 
Hinge- joint,  56 
Hip-joint,   55 
Hydrochloric  acid,  105 
Hvdrophobia,   204 
Hygiene,  10 
Hypermetropic  eye,  306 


Heocolic  valve,   112 

Ilium,  106 

Image  on  retina,  312 

Incisors,  98 

Inferior  vena  cava,   139 

Inhalation.  171 

Inspired  air,   177 

Internal  ear,  328 

Involuntary  muscles,  66 

Iris,  300 

Irregular  bones,  38 


Jejunum,    106 

Joints,  53 

health  of,  57 
kinds  of,  55 
structure  of.  53 


K 


Kidnevs.  223 


Lachrymal  gland,   317 
Lacteal,    108 
Lacuna^,  46 
Large  intestine,   112 

action  of,  112 
Larynx,  165 
Levers.   02 


Life,  5 

Ligaments,  54 
Light,  296 
Liver,  108 

action  of,  129 
Lobes  of  brain,  241 
Lock-jaw,  198 
Long  bones,  36 
Lungs,   169 

as  excretory  organ,   222 

capacity  of,  174 
Lymph,  138 
Lymphatic  nodes,   141 
Lymphatics,    140 

M 

Malpighian  bodies,  226 
^lammal,  7 
Z\larrow,  48 
Mastication,  97,   113 
Matter  and  life,  5 
Medulla  oblongata,  243 

function  of,  263 
Medullary  layer,  225 
Medullary  sheath,  235 
Medullated   nerve-fibre,   237 
Membranous  labyrinth,  331 
Meninges,  238 
Mesentery,  106 
Middle  ear,  323 
Modiolus,  330 
Molars,  98 

Movements  of  the  eyes,  307 
Mucous  membrane,  30 
Muscles,  60 

attachment  of,  61 

development  of,  69,  70 

food  of,   70 

kinds  of,  65 

of  the  eyes,  308 

skill  of,  73 


INDKX 


363 


Muscles,  stnicturo  of,  07 
Muscular  tissue,  27 
Mj'opic  eye,  305 

N 
Nails,  214 

care  of,  21!) 
Nerve-cell,  234 
Nerve-centres,  258 
Nerve  endiiifjs,  2.")! 
Nerves,  243 

functions   of,   209 
Nervous  system,   233 

divisions  of,  233 
Nervous  tissue,  27,  237 

nutrition  of,   271 
Neuroglia,  238 
Neurilemma,  235 
Neuron,  235 
Nitrogen,  176 

Nitrogenous  equilibrium,  228 
Nodes,  237 
Nose,  342 
Nostrils,  165 
Nucleus,  18 

O 

Odontoid  process,  40 
Q^]sophagus,  102 
Olfactory  region,  344 
Opium,  290 
Optic  nerves,  313 
Organ  of  C'orti,  335 
Organs,  28 

Origin  of  muscles,  61 
Osmosis,  95 
Osseous  tissue,  27 
Osseous  labyrinth,  329 
Otoliths,  332 
Oval  window,  330 
Oxidation,  82 


Oxygen,  175 
Ozone,  175 


Piicininn  corpuscles,  341 
Pancreas,   110 
Pancreatic  juice.   111 
Patent  medicines,  290 
Pelvis,  41 

Pelvis  of  kidney,  224 
Pepsin,   105 
Peptone,   105 
Pericardium,    131 
Perilymph,  331 
Perineurium,  244 
Periosteum,  47 
Peristaltic  motion,   105 
Peritoneum,  103 
Perspiration,  211 
Pharjnix,   101 
Physical  culture,    72 
Physiology,  9 
Pia  mater,  238 
Pinna  of  ear,  322 
Pivot- joint,  50 
Pleura,  170 
Pleural  cavity,  171 
Plexus  of  nerves,  254 
Pneumogastric  nerves,  247 
Pons,  242 

function  of,  203 
Pores,  210 

Portal  circulation,  151 
Proteid,  83,  80 
Protozoa,  0 

Pulmonary  artery,    137 
Pulmonary  circulation,  152 
Pulse,  147 
Pus,  203 

Pyloric  orifice,   102 
Pyramids  of  Malpighi,  225 


3G4 


IXDEX 


R 

Eacemose  gland.    100 

Red  corpuscles,  142 

Keflex  action,  2G3 

advantage  of,  260 
education  of,  267 

Refraction  of  light,  298 

Renal  circulation,   152 

Rennin,   105 

Respiration,   162 

experiments  on,   189 
hygiene  of,   179 
organs  of,  165 
use  of,   164 

Retina,  309 

Ribs,  42 

Rickets.  49 

Rods,   311 

Round  window.  330.  336 


Sacculus.  331 

Sacrum,  40 

Salivary  glands,  100 

Sarcolemma,  67 

Secretion.  221 

Semicircular  canals,  330,  337 

Semilunar  valves,   134 

Serous  membrane,   29 

Short  bones,  37 

Size  of  brain,  239,  262 

Skeletal  muscles,  60 

Skeleton,    34 

Skin 

as  an  excretory  organ,  223 

as  a  protection,  202 

color  of,  208 

hygiene  of,  214 

layers  of,  207 

use  of,  206 
Sleep,  276 


^mall  intestine,   105 

digestion  in,  110 
Smell,  342 
Soft  palate,  101 
Solar  plexus,  256 
Sound,  296 
Sound  of  heart,    154 
Sound-waves,  320 
Special  senses,  293 
Spinal   cord,  247 
Spinal  nerves,  249 
Spleen.   141 
Sprains,  58 
Stomach,   102 

health  of,   114 
Striated  muscle,  68 
Superior  vena  cava,  139 
Suture,  38 
Sweat-glands.   210 
Sympathetic     nervous     system, 

255 
SynoA'ia,    54 

Systemic  circulation,    151 
Systems,  28 


Tactile  corpuscles,  339 

Tartar,  113 

Taste,  345 

Taste-buds,  347 

Tears,  317 

Teeth,  97 

care  of,  113 

Temperature  of  body,  211 

Tetanus,  198 

Thoracic  duct,  129 

Thorax,  30 

Tissue,  23 

Tobacco 

effect  on  circulation,  158 
effect  on  respiration,  187 


INDEX 


365 


Tobacco 

effect  oil  tlie  nerves,  288 
Tonsils,  101 
Touch,  339 
Trachea,  167 
Trichinie,  1»0 
Tuberculosis,   185,   109 
Tympanum,   323 
Typhoid  fever,  201 

U 
Urea,  228 
Ureter,  227 

Uriniferous  tubules,  226 
Utricle,  331 
U\-ula,  101 


Vagi,  247 

Vahnilae  conniventes,    106 


Veins,  139 
Ventilation,  180 
Ventricles,   132 
Vertebral  column,  39 
Vertebrates,  7 

classes  of,  7 
Villi,  106 
\'oeal  cords,  lOi 
Voluntar}'  muscles,  65 

w 

Water,  123 

Wheat,  86 

White  corpuscles,   144,  203 

Work  of  heart,  154 


Yeast,  193.  196 
Yellow  spot,  311 


THE   END 


«r- 


SEP  11 


1928 


!  i 


wr 


llUit! 


